Look, all you have to do is memorize a couple thousand pages of reagents and their products. It's easy, bro. Don't even think about all the pressure/temperature/volume/math-like-Le-Chatelier's-Principle stuff, that's physics, bro.
Those water flavor squirts, mio or crystal light type stuff. I'll drink plain water over just about everything else (egg nog is the weakness and exception right now...), but the various lemonades or fruit flavors are always nice to have around. I wouldn't be surprised if something in their composition is not good for you.
A slightly more titillating answer would be lube. You're putting something on a mucous membrane, and it's almost guaranteed that some will be absorbed or ingested.
Maybe it's just me, but I don't want the cops breaking into my house to investigate the smell of my dinner. Curry is delicious, and you know how pigs are about food. We've already (mostly) gotten rid of scent being a reason to search with the ingresses we've made for weed. Let's avoid odor being a definitive reason to search people's property again.
Look, all you have to do is memorize a couple thousand pages of reagents and their products. It's easy, bro. Don't even think about all the pressure/temperature/volume/math-like-Le-Chatelier's-Principle stuff, that's physics, bro.