Drinking water. Don't flush the toilet because you might eventually need the water in the tank too.

FYI like 90% of your comments are flagged dead, but I read through them and think they're hilarious. You might want to create a new account.

I've never understood this. What do you do when you need to defecate?

Poo in a bucket, put a lid on it. If the alternative is eventually dying of thirst or having to venture out into a contaminated neighbourhood, necessity compels.