You should buy your films from somewhere which sells a lot of it and keeps it properly (in a fridge). Generally a super-sized Jessops will be OK, but if you haven't got a good one then it's up to London and into one of the monster camera shops in the West End. Check the expiry date on the film - the further into the future, the better.
Keep the film cool, preferably refrigerated, in a low moisture environment until you leave. A tupperware box in the fridge does the job well. Choice of film is of course personal and can be argued to death, but I like Velvia (50) and Provia (100) colour for this type of environment.
Don't worry too much about the heat and humidity - you can't do anything about this! Just ensure that you take the normal sensible precautions - avoid changing films when it's raining or when you're on the beach. Don't leave your kit in the direct sunshine, especially the car boot when it's a hot day.
If your kit does stop working whilst out and about, DON'T PANIC! get into an air-conditioned bar and have a few drinks and wait for it to cool off and then test it before panicking officially and ripping everything apart and losing your film. I find that semi-tropical environments and photography in hot environments will jam the shutter on almost everything electronic after a few hours. My trusty manual SLRs are pretty much the best in these situations, but expect a few quirks with auto-focus and such on a complex camera.
Good luck, you'll be fine!
Rob