TravelJohn Disposable Urinal Bags – Road Trip Essentials for Men, Women & Kids – Odorless Leakproof Portable Urine Bags – Ideal for Camping, Emergencies & Long Car Rides (TJ1A-C)

The Travel John is the best device I've ever used when needing to urinate in a car or when I was living in a tent. There is a some powdery gel in the device that when it gets wet turns into a super thick gel ball that eliminates odors and prevents spills. After a couple uses, you seal it and toss it. There are some biodegradable versions but it is probably best used for emergencies and when you first getting used to car living. Travel John link