I don't even want to know the answer because it'll be less entertaining than lemmy's collective imagination.
As for the question: I think your biggest problem is going to be inducing a proper clearout shortly before you go on your trip. Maybe laxatives?
Edit: I just realized, is the reason you don't want to go despite having toiles available stuff like hemorrhoids or an anal fissure? Because if so, there are creams for that my friend.
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....