Reddit mentions of MSR IsoPro Fuel 8 oz.

How small? Iso canister stoves are basically the standard for hiking - something like this as a small, cheap and light stove, which screws straight on to a fuel canister like this. You can also opt for white fuel stoves like this one if international fuel availability or extreme cold weather performance matters. They use refillable fuel bottles that come in various sizes to meet your need. Finally, alcohol stoves are fairly popular as a lightweight, if slower, option - I have this one, though plenty of people make their own from aluminum or tin cans. Fuel can be carried in pretty much whatever, since you just pour some into the stove before use.