in regards to 1 or 2 piece
i can relate to bellytank's & ascend charlie's response
might be a little off topic with this one, but i recall being on exercise in NT with armoured support, on of the APC crewman wanders off into the scrub with his entrenching tool & toilet roll over his shoulder & rifle in hand.
a few minutes later he returned with his rifle, e-tool, his boots & a smile.
seems he didn't quite arrange his tank suit prior to "jettisoning his package"
it wasn't until he had finished his business & turned around to fill in his 'catscrape' that he realised something was definitley missing...needless to say he deposited more than just organic waste that day.
Perhaps a 1 piece flight suit might be inherently susceptable to a similar predicament if you weren't too careful, & of course if you have appropriate ablutions at your disposal, this reduces the risk factor substantially.