You need one of these beauts and a bucket in your service rig. Should have tall enough sides for a little modesty in the bed.
My favorite turd spot on deployments was the dozer blade. Sit on the blade support bar, lean against the blade with cheeks out. Relaxing, relatively protected spot to release the days problems. Lift blade, back up, blade down and keep dozin'.
Once had to shit in a parking lot on MCRD San Diego. I'd park my pickup there and get a cab to the airport when going on leave. Get back to the truck and it hits me. I have no clue if there's unlocked bathrooms near this lot and I'm panicing in the dark as it rains. Squat by the rear tire in the rain and left a mostly liquid present. Hope it washed away before morning.
Also TP in all vehicles, had to drop presents in a few tree lines. Even once at work, I wasn't going to make it the 100 yards to the house from the shed. Grabbed a roll of paper towels from the bench and hustled to the tree line 10 yards, barely made it.
Friends were asking why I don't stop for fast food on my two day drives to Tejas. I'm not going to risk it miles from a clean throne. Pb&Js as I drive, can eat plenty of Mexican food and Whattaburger when I get to Corpus.