I recommend eating a lot of cheese and absolutely NO fiber. Not sure if it will make you sweat less, but I'm pretty sure if I ate only cheese for 3 days, it wouldn't be too hard to wait till the end of it to poop. In fact, I may need some help at that point... maybe you should eat some fiber like a couple hours before you do plan on trying to poop, and also drink lots of water at that point, too. I personally find cheese very "helpful" in getting myself constipated, and fiber + water to be a great way to smoothen the pooping process.
I need to survive for 3 days without pooping, and eating as little as possible. I can pee, but not very often. It can't take up too much space. What food do I pack?
Please don't ask why I need this....