Just found this thread and didn't read through all 18 pages so forgive me if this has been mentioned already, but if somebody hasn't stolen the trash can from your truck, you can use that can lined with a couple DR bags as an emergency crapper!
I always carry a roll of toilet paper, which can also double as Kleenex, just in case and recently graduated to the moist, flushable wipes, which I did see mentioned earlier. They are so much easier on the ol'browneye. (see what I did there!) And an extra pair of underwear comes in handy in case the DR bags are sticking closed and you can't get them open in time or what you thought was going to be a fart, isn't. I carry an extra pair of shorts for days when I lift correctly and rip them out from zipper to belt loop but now that I think about it, they would also help save the day in the "can't get the DR bags open in time" scenario! If you do decide to use this driver hack I strongly advise that you dispose of said DR bag ASAP as even after using 5 bags, that trash can will smell like a blue room for hours! (Not to mention the back of your truck.) And yes, I do carry hand sanitizer for easy disinfecting.