I keep Simethicone on hand….but thankfully have never had to use it yet.
I thought about buying some Critical Care to have on hand (my vet clinic/work does not keep it in stock) but I know there are other clinics about 30 minutes away that I can buy it from. The expiration date was the main reason I have not bought any. If I could not drive and get it- had to order and ship it- then I would have some on hand.
One thing that I would recommend having on hand since bunnies are notorious for sensitive eyes (in my opinion) is a bottle of saline eye wash- just plain old stuff you buy from the pharmacy. Obviously you have to decide when is approp to use- but I have it on hand (and have never had to use it) for my active dogs. But if it looks like your bunny has a external eye irritant- i.e dust or hay- you can wrap your bunny in a towel and rinse the eye/face.
I will try to think of other things that would be useful in a pinch.
Thankfully I live in a larger area that has 24 hour grocery stores 5 minutes from home. But where I grew up- there was nothing open after 10pm except gas stations and liquor stores.