while on the road in easy reach in an organizer on the passenger seat. there are many styles and varieties to choose from. i picked a scrap-booking tote with a ton of pockets. i limit myself to the things that fit and review the contents regularly removing anything that i don't need. i can quickly move the tote to the back seat or trunk when i have a passenger or i don't want to look at the items.
put it in the trunk. all the items that you need regularly but never need in reach can go in the trunk. think of the trunk as your portable supply closet for extra 