Excellent! I know I’m not the only Big Island lover who will be happy to throw endless ideas at you.
So … where are you staying? The Big Island is, well … BIG … and it makes sense to suggest things mostly near where you are staying, plus a day trip or two that ventures farther afield in a geographically practical way.
.
We’re staying between Hilo and a volcano, near the beach.
Do you dive? We dove on the Kona side but had a fantabulous time with the Manta Night dive. Still ranks as one of the most amazing experiences (and you spend most of it sitting on your butt on the floor of the ocean. We used Big Island Divers and were very very happy with their staff.
Volcano National Park is going to be a big part of your trip based on your location. What’s available to see fluctuates so check in on their website for up to date situation reports on lava flows.
There is also a bus trip to the top of Mauna Kea (again ours left from Kona but should be one from Hilo too) We went from sunny ocean to sunset over the snow topped mountain.
Nexus is $50 for 5 years and it’s totally and completely worth it. We got ours just before our trip to Hawaii and walking past two entire rooms full of a snaking line of people waiting to get through security was enough to convince me that we’re never not renewing this. I’ve had trips where I’ve gone from curb to sitting at the gate with a drink in my hand in under 15 mins. It’s not quite that fast anymore since more and more people are signing up but it’s still way better than waiting in the non expedited line.
Right now for Canadians when you get Nexus they throw in Global Entry for free. Not sure if it’s the same for Americans but worth looking into.
In that case my suggestions in post #47 are reasonably close by. Also, I don’t know why I didn’t mention the Pana’ewa Zoo, which is no great shakes compared to world-class zoo facilities but is an extremely pleasant place to stroll through. They have two new tigers, too, one white and one orange, to replace the beloved Namaste, their white tiger who finally died of old age.
I agree with Moonlitherial that Hawaii Volcanoes National Park will be a significant part of your visit. At the moment (as it has been for several years, though things could change quickly), there is great viewing of lava flowing into the ocean, best seen at nightfall, outside the park at Kalapana. If an 8-mile-round-trip walk, or a similar distance on rented trail bikes, is out, then you’ll have to skip this one. But assuming you don’t mind a little exertion (and it’s not hard; the going is pretty flat), this is a memorable sight.
South of Volcano, you may want to check out Punalu’u Beach, a particularly beautiful black sand beach (and a nice place to picnic). You could do that on the way to or from South Point (a longish but beautiful drive from Volcano). However, the best thing to do at South Point is to visit Green Sands Beach, and unless you’re a local with a 4WD vehicle, that means another walk. As is usually the case on the Big Island, it is abso-fucking-lutely gorgeous, but if even a modest hike is out of the question, it won’t work.
One site I probably recommend skipping is the Mauna Loa factory tour (it’s sort of across the street from the zoo). We went there years ago, thinking that even if the tour of the factory was not a big thrill, we’d be able to buy macadamia nuts more cheaply there. Nope. The nuts are just as expensive as in the grocery store. And the factory is only in operation for a couple of months a year, so the rest of the time there is just this lame video of “how nuts are harvested,” reminiscent of what a substitute 5th grade teacher would have had you watch in 1974.
I say “probably” skip the factory because I think it actually does process nuts in October, and IIRC it’s free. So if you are in the area already with some spare time, you could check it out just for shit 'n giggles. (If it’s awesome, let me know so I can update myself.)
Unfortunately I think Moonlitherial may be wrong about there being a Hilo-side pick-up for the Mauna Kea tour, but don’t take my word for it; I hope I am wrong. Just be aware that there may not be. It will make for a REALLY long day if you have to go from the Hilo side over to Queen’s Market in Waikoloa (where I know there is a pick-up), take the tour, and then drive back to Hilo-side late at night.
I’ll post again later if I think of more stuff.
Used to. Last dive was a wreck off of Nanaimo. It’s a bit of a chore to dive up here, and cold too. If you know anyone who wants a US Divers UDS-1, let me know. I never got round to using it. 
We also did the night Manta snorkel trip. We booked with Aloha Ocean fka Sea Hawaii. Just incredible, even though we couldn’t sit on our butts.
Also near Hilo is Zip Isle Ziplining. Haven’t personally been to this one, but I’ve ziplined several times and it’s always a blast.
Make lunch or dinner reservations at Kilauea Lodge, which is a few minutes outside of VNP. It gets booked early, so make them before you leave.
Resurrecting this thread to recommend Bri’s Big Island BBQ. The link goes to Yelp! reviews, but you can also check his Facebook page for up-to-date info on when and where he will be.
Brian is doing his best to establish a mouth-wateringly wonderful pop-up restaurant business based on classic BBQ dishes, Hawaiian favorites (mac salad is a must for plate lunches), and his own incredibly delicious sensibilities. I met him at the beginning of the summer and chatted about food with him; after hearing him talk with passion and precision about his cooking, I couldn’t wait to try his food. Alas, he then went through some health and other problems that caused him to not sell his food for a while, so I didn’t get to try his cooking right away.
He just came back, though, and I promise you - his food is UNBELIEVABLY GOOD, and very reasonably priced. We went to his spot (outside Mr. Ed’s in Honomu) two nights in a row, that’s how wonderful his food is.
Please make an effort, if you can, to try out his food. He’s a good guy and deserves the custom. You will not regret it because his food is to die for.
I’ll try to talk The Wife into it. 
Yet another resurrection before it is too late, to add a couple more Hilo possibilities. Neither one necessarily warrants a special trip to Hilo, but it depends - check out the current exhibits, workshops, and programs on line, and maybe there will be something going on that appeals to you:
East Hawaii Cultural Center (https://www.ehcc.org)
Imiloa Astronomy Center (http://www.imiloahawaii.org)
I’m quite the Hilo booster, I am. The Chamber of Commerce should hire me.
When we were on the big island, we enjoyed driving through Kona coffee country and seeing how coffee is grown. It’s uphill from Kailua Kona, and you can drive from one end to the other of the coffee-planting area in less than an hour.
Midway through the drive, stop at the Holuakoa Cafe and Espresso Bar for some Kona coffee or espresso, and drink it a few yards from the edge of the nearest coffee plantation.
I’m starting to wonder if I’m going to enjoy this trip. The company expects revenues from our data to fall in the first quarter of 2018, and the president is looking at me with an eye to cutting costs. 
Not sure if this will be helpful, but I live in Minneapolis. For a period of time, Delta eliminated the non-stop from Minneapolis to Honolulu. So, to get us to Hawaii cheaply, we took a discount flight to Las Vegas, grabbed out bags, then checked them in for a Hawaiian Airlines direct flight from Las Vegas to Honolulu. It was a red-eye flight, but going through all of that saved us a bunch of money.
Not surprising. There is a weird Las Vegas-Hawaii connection (speaking in terms of cultural phenomena, not airline routes, although the first leads to the second).
Johnny L.A., here’s hoping stress doesn’t ruin your vacation. I hope everything turns out okay with respect to your office, and that you can relax and enjoy your time on the Big Island.
.
I liked the Maku’u Farmers Market more than Hilo’s but both are good.
Ken’s house of Pancakes is a fun meal.
The KTA South of Hilo has a good deli / hot food counter.
If you see a guy BBQ-ing chicken on a huge towable grille in a parking lot stop & buy one.
If you’re cooking for yourself try Portuguese sausage & eggs for breakfast.
Try Kmart or Costco for souvenir type stuff.
Hawaiians love Vegas, so it’s a big route. There’s even at least one ABC Store there, plus a restaurant or two that serves Loco Moco.
L&L Barbeques are on the mainland now. I’ve seen Loco Moco on menus in a quite a few places.
Not downplaying the HI-LV connection. I found it odd that so many Hawaiians liked to go to Vegas. Weird.
Not so weird. Lots of ethnic Chinese here, and one stereotype I learned holds true to a large extent while living abroad is Chinese LOVE to gamble. Filipinos too, and there are lots of ethnic Filipinos here. One little old Filipina neighbor of ours hits Vegas at least twice a year, often more.
We loved the Hawaii Tropical Botanical Garden, just a few miles from Hilo.
Oh, yeah, I forgot. We saw this, too, and we loved it. Lots of beautiful and bizarre plants and flowers. I love heliconia, and had no idea there were so many varieties. It’s in a very rainy area, but the garden provides umbrellas if it should happen to be pouring (which it was when we visited).
We spent two weeks in Hawaii in August 2016. I wasn’t sure if I was going to be able to convince my wife to go back, so I tried to see and do as much as we could. We spent 3 nights in Maui, 3 nights on the Big Island, and 7 nights at the Disney resort (Aulani) on Oahu.
For our short time on the Big Island, we flew into Hilo from Maui, and stayed one night in a B&B near Volcano National Park. We saw the glow of the volcano crater at night from the park lookout, and toured the park and old lava flows the next day. I would have liked to have made it out to where the lava was actually flowing, but we didn’t have time. We then made our way to a beautiful hotel on the Kohala Coast on the west side of the island. My son and I went scuba diving there, which was a great place to dive. The dives were relatively shallow (20-40 feet), so each dive was over an hour. I thought about doing the manta ray night dive, but the timing didn’t work out due to our short time there. (A friend of mine did that dive this past June and raved about it, posting some great video on Facebook.) We then flew out of Kona so that we didn’t have to drive back across the island.
Overall, we really liked the Big Island. The lava flows everywhere are really amazing. I’d like to go back and spend more time there in the future.