Land?...but that would be too obvious for you. I assume you want to remain airborne. Carry a portable john if you've been drinking a diuretic fluid. They sell them through Sporty's. One poster on another thread told of a story where he peed into a ziplock bag and after landing accidentally leaned over onto it and it burst all over himself. If you've got a barf bag, which you should carry for pax or yourself, you could also use that.
Worst case scenario, pee in your pants. By the time you land it'll be dry. Or at least remain inside until it does.
Some adult diapers like depends may be in order as well.