I wore my armor for around 36 combined hours at SDCC, and only once did I have to take a wizz while wearing it. Was actually kinda funny, cause Beviin Verhayce from the Mercs AZ clan (a.k.a DSG Mandos) and I had to make a pitstop after getting Karen Traviss to her Star Wars panel. I'm sure that people don't expect to walk into a bathroom and see 2 guys in mando armor using urinals. I think out buddy Anthony got a funny pic of us "Primping" in the bathroom mirror.
I tend not to eat when in armor, which reduces the need to have to do #2. I do drink plenty of water and actually carry emergency water packs for myself and my brethren in armor, cause it doesn't matter what club your in if you fall out from dehydration. The key is to time your liquid intake so that you sweat it out before it reaches your bladder. I tend to drink a normal 20oz bottle of water every 2 hours if i'm inside where it's cool, or 1 every 1-1.5 hours if I'm outside and it's hot.
This is usually PLENTY to keep my body hydrated enough, but everyone's body is different...so you need to find out what works for you. If you need to eat, then carry around nuts/trail mix/granola bars as the fiber makes these hard to digest fast. You'll also stay fuller longer, and when you do gotta go...it'll be a good one LOL!! Stay away from greasy or fried foods and dairy products if you can help it. These seem to cause havok with your body if it's already being stressed by armor and heat.