There's really very little that you can do at home for an ill bunny - rabbits hide illness very well (because they are prey animals so they try not to draw attention to their illness as a predator is more likely to go for them) which means that whenever you notice a poorly rabbit, it is likely to be much more poorly than you might think. Of course some people have rabbits with ongoing or chronic problems and their vet may feel it is appropriate to give them medicines to use at home, but it's the exception rather than the rule, meaning that the bunny first aid box is really of limited value to most people.
There seem to be different schools of thought on hairballs - i.e. does hair build up and cause a blockage, or do rabbits with sluggish intestines result in a build up of hair and hence a blockage? Personally in most average buns, I think it's more often the latter.
You can buy pineapple and papaya 'treats' for buns which are supposed to contain an enzyme which breaks down hair...similarly fresh (not heat treated) pineapple or papaya have a similar effect. However they are very sugary so can have an adverse effect on a rabbit which already has a compromised digestive system. Some people feed one of these treats or a small chunk of fresh pineapple daily when the rabbits are moulting. Obviously regular grooming to remove loose fur, especially when moulting, will also help to reduce the risk of them ingesting lots of fur. Personally I think that the best way to prevent hairballs is to keep the gut in good condition by feeding a high fibre diet and to make sure that the rabbits are kept well hydrated by having fresh, clean water available and regular grass and portions of vegetables.
Infacol (simethicone) is indeed the stuff you buy for babies from the chemist. It can be useful to help relieve bloat because it draws small gas bubbles together into a large bubble and can help them to pass. However, this really is one of those things that I think should only be used in conjunction with a vet visit. Bloated rabbits really require painkiller and investigation, and can go into stasis and die very quickly if they are not given prompt veterinary attention depending on the cause - hence my reluctance to suggest that people self administer. It probably doesn't hurt to have some in the house but if a rabbit is showing signs of possibly needing it, I would still want to get onto the vet first. You can then always ask the vet if it's ok for you to give some infacol while you are waiting to get the bunny to the vets as it may help a little, but it should not be used as a substitute. We've seen too many 'wait and see's' result in the death of a bunny where the bun has appeared bloated or in stasis
Hope that helps!