I’m halfway through a short work assignment in Singapore. Here’s what I’ve seen/done so far:
Marina Bay Sands
Gardens by the Bay
Botanic Garden (sort of; will go back)
Little India + Mustafa Centre
Approx. 1.3 million shopping malls
I would like to go to the zoo but I’m afraid that I will pass out from the heat and humidity. What are the “can’t miss” attractions in SG that I should see before I leave, possibly never to return?
I hope you’re eating everything in sight. That’s the best thing to do in Singapore. Off the top of my head, you shouldn’t leave until you’ve had laksa, as many satay as you can cram into your gullet, chilli crab, that whole-fish grill/hotpot thing that’s a new trend, bah kut teh, kaya toast with eggs, durian, roti prata… oh man. Controversially, I will recommend skipping the Haianese chicken rice. Most white people find it bland.
Did you see the otters at Gardens by the Bay? There’s a family of wild small-clawed otters that are very used to people and great fun to watch. There’s also amazing birding, if you’re into that. For captive birds, Jurong Bird Park is well-known too.
The orchids in the Bot Gardens are amazing, make sure you find them.
Can you sing this in a karaoke bar?
Funny enough, second night here someone brought me out for hainanese chicken rice and yes, I did find it bland 
I went to Jumbo a few nights ago because a colleague was extremely (!) enthusiastic about their chili crab. I thought it was ok (but I am not a huge fan of crab to begin with.) I had the cereal prawn which was pretty tasty.
On a side note, it’s a good thing I can expense all of my food here because OMG.
If it’s too hot for visiting the Zoo during the day, consider a Night Safari; lots of animals that are not active during the day are out and moving about there (be sure to visit the Bat habitat).
Eat, eat and eat. Then go to Raffles to have a drink before eating some more. Get a copy of the Makan Sutra and eat.
Zoo
Night safari
More restaurants than you can shake a stick at - chili crab at East coast seafood, I recall a churrascaria somewhere in the western suburbs
Sentosa (meh on a global resort scale, although the fort was interesting).
Shopping malls
Jurong bird park
My experience is from the 1990s but I imagine little has changed. Sim Lim Square used to be the place for anything new and electronic and for any pirated software on CD you could imagine. I think the CD merchants were shut down not long after my trips.
The bat habitat at the night safari caused an interesting falling out between me and my wife. I was very interested, she was not so I will went thru and could not find her at the other end. Turns out she hired a cab back to the hotel and had it charged to our room, and it took me maybe an hour and a few anxious phone calls to figure this out.
The zoo is interesting because there are no bars, and both the habitat and the grounds have tall trees. We were walking along one of the paths near the ape enclosures when a chimpanzee suddenly appeared a few meters down the path and ambled down away from us (not an indigenous creature and apparently an escape).
I did a few business trips aside from the trips with my wife. My work host said Singaporeans don’t do many outdoor activities because it’s so freaking hot and it rains so hard in the afternoons.
Night Zoo for sure!
Chili crab and Black pepper crab
The Hard Rock Café is one of the best in the world too!
In 1984, I lived on Scotts Road, just down from Newton Circus (I see from Google Maps that my apartment building is now gone and a Sheraton is now there). I would walk up to the Circus for food on a regular basis. Literally everything imaginable was being cooked and served there, and it was all delicious.
The Chinese and Japanese Gardens were incredibly beautiful.
I don’t know if this is still done, but there used to be weekend excursions that you could book to Kuala Lumpur. You would meet Friday evening, they would bus you over the bridge to the airport in Johor Bahru. You then flew up to KL and spent the weekend at a hotel/casino. On Sunday evening, you reversed the process. Those were lots of fun.
Singapore is remarkably changed since the 80’s and nineties, like a ton I find. Orchards Rd is all Dior, Channel, Manola Bl, etc, etc, it’s one endless string of extremely high end shops now, amazing. A million more xpats, and they’re everywhere you go. Tons of new infrastructure, including roadways under the ocean, a subway, lots of green and solar development including beautiful water resovoirs. And tons more public art, it’s everywhere. Bugis street is unrecognisable from back in the day, the rare stone collection is gone, as is the sate club and a few other things. Exit and entry is all via facial recognition software these days, and Changi gets better every year, now they have a jungle experience! It’s still #1 though, of course.
If you’re into BDSM, I’ve heard you can get a free caning if you commit some vandalism…
I stayed at that Sheraton once or twice, then a series of stays at the ANA hotel on Nassim Hill near the US embassy and botanic garden. Interestingly, I see from Google Maps that the ANA Hotel is now gone and a block of apartments is now there. 
My instinctive thought when I read this was “then where the hell can you get a drink?”
Hmm. I may have a problem.
My now wife lived on Orchard back in the 80’s and it wasn’t too shabby back then. Private elevator to the apartment… driver, etc. My kids were there just a few months ago and they agreed that it had changed drastically from when they were last there maybe 9 or 10 years ago.
Excellent suggestions upthread. If you like museums (I do), the Asian Civilizations Museum and the Singapore National Museum are wonderful - you can check to see what special exhibits are going now and figure out if any of them interest you.
Has anyone mentioned eating yet?
Yeah, Singapore has great museums. The botanical gardens are great, especially in the evenings and the restaurant in the gardens used to be quite good: http://thehalia.com/
Also, check out Archipelago Brewery which has a number of brew pubs in the city: https://archipelagobrewery.com/
and we did a number of walking tours through this outfit that we enjoyed, I think it was Hello Singapore. We have also used Context Travel for walking tours in a number of cities, and they do Singapore: https://www.contexttravel.com
I’m staying on Orchard, amidst the zillion high-end stores! Seriously, nowhere else have I seen so many Rolex and Louis Vuitton shops.
I went to the ArtScience Museum and the Singapore Art Museum this weekend. In the former, the room full of LEDs is … bizarrely transcendent? Probably worth the price of admission alone.
I also went through Chinatown but either there’s not much to see or I missed it completely; it was really hot this weekend and I gave up pretty quickly.
Awesome authentic Indian food in Little India, Serangoon Road. Plus: cheapest dining in Singapore.
You Have to get off Orchard and explore the city more.