I have a fair amount of stuff in my car, as I tend to go to fairly remote locations to start some of my mountain bike rides. On one of my rides I did an endo and got some 'trail' rash, had nothing to cover it up with or adequately clean it out, and an hour back to the car, another hour back home at which point it was already dried out and crusty. Ended up with an infection and an iodine scrub by a nurse... Which is why I have my car stocked.
I have a pack with most of the stuff people have mentioned, gauze, tegaderm, large band aids, non stick pads, sports wrap (or vet wrap, cheaper), those wet antibiotic wipes you can clean with, some ibuprofen, duct tape, scissors, etc. Also a CPR face mask which I hope I never need!
Specialized Oura or Romin Evo Saddles