Avoid anything that is likely to leave crumbs. Will you have room for an easily accessable ice chest? If so you can pack things in containers that would otherwise be packed in wrappers.
Sunflower seeds in the shell. Long drives can be boring and I find the effort required to extract that tiny little reward is enough of a diversion to keep me from falling asleep, or just help pass the time.
Also lots of bottled water. Drinking a lot of water means more rest stops, but I need to stop every couple of hours anyway to stretch my legs or I get so stiff I can barely walk.
We just completed a 5000 mile road trip last month. In the cooler, we had
apples
grapes
various kinds of nuts
yogurt
cheese
lunchmeat (ham and/or salami)
cheese
bread
condiments
bottled water
Breakfast generally consisted of one or more of the following: the free buffet at the hotel, leftovers from the previous night’s dinner, or yogurt and walnuts. Lunch was generally sandwiches, and dinner was at a restaurant. The fruit and nuts made for great on-the-go snacks.
If you have a decent-sized cooler, then make your own ice beforehand with small, kid-sized plastic cups. 2-4 are good. The ice keeps much longer.
Cut up some celery & carrots & toss those in a baggy or 2.
Bananas are handy for cramps. (I have never had to deal with squished bananas in my car but I dump the peels at the 1st refuelling stop however.)
I usually eat a filling salad before I go so I have a steady source of energy & I’ll hit the soda or tea later on.
Soda = fewer bathroom breaks. I usually balance the soda w/ water or I get headaches.
If you get tired easily, put some 5-hour energy drinks in a handy spot, same for aspirin & sunblock (driver’s tan).
My gear shifter’s in the center hump between the driver’s & passenger’s side so I hang a handy plastic bag to put my trash in so I can tie it up & dump it in 1 go & so my trash is all in 1 place.
I let the road decide. I ate at white castle, long john silvers, and lots of other restaurants that I don’t have in my city. The one I missed was Olive Garden’s all you can eat special. I missed it by two weeks before they switched to the buy one, get one free model. I also missed Sonics, even though I passed like 20 of them. I kept telling myself I’ll stop at the next one, and then they stopped showing up.
Not really something you’d want to do, but when I was a kid, two adults and five kids would travel to Florida, in August, in a sedan without air conditioning. My mom had a bag about the size of a cloth grocery bag that would be half filled with Brach’s pick-a-mix. At home, we were limited to 5 pieces a night as a snack. On the trip, we would get five pieces every couple of hours just to keep us quiet (if you’re noisy, no more candy). We thought we were eating like kings and my dad didn’t kill any of us:D.