My wife has purchased disposable travel urinals before, but they cost $1.50 to $2 each. This is cheaper.
Step 1: Supplies
1 disposable cup (I use old ones destined for the garbage)
1 plastic newspaper sleeve (again re-used). Alternatively you could use the little baggies made for dog poop.
1 diaper booster pad, or bladder control pad. Alternatively, you could repurpose unused diapers your child has outgrown
tape (duct or shipping tape)