Day to day, my skateboard is ALWAYS in the back, I add the rubbermaid tote for off-roading which contains, at the moment:
-recovery strap
-12v "tornado" compressor -best small one I've seen
-110 pc toolkit
-2 jugs (8L) of water
-folding shovel
-2 GMRS
-a pile of energy bars
-spare clevis tow hook
-roll of duct tape
-tie downs
Plus extra food, clothing, sleeping bags, recreationables