You're going to get LOTs of answers to this one.

I have used my on-board emergency supplies a dozen times to help others for every one time I needed to help myself. Make sure your spare has air and the tire-changing tools are complete. After that, in order of what I have needed and how important it was:

#1 Fire Extinguisher
#2 Flares (4-6)
#3 20' of 1000 lb or better nylon rope
#4 Large First Aid Kit
#5 Water (just a pint or so)
#6 Butane cigarette Lighter
#7 Sharp knife
#8 Toilette Paper (don't ask)
#9 Pliers w/wire cutters
#10 Screwdriver with multiple tips
#11 Grease Rag
#12 10/12mm open-end combination wrench
#13 12/13mm open-end combination wrench
#14 Old wire coat hangar
#15 Large waterproof camping lantern
#16 Spark Plug Wrench

If I am on a long trip, I carry my trusty John Deere hand-carried tool box that has a full set of metric combination wrenches including 18mm, metric socket set, and other standard tools odd fuses and electrical connectors, nuts and bolts etc.

The right-hand storage pocket in the back carries odd used-but-still functional parts like an old timing belt, old V belts, a couple of old spark plugs. If I had an extra functional fuel pump relay, I would carry it.

You may have noted that 40 years of driving has taught me that tools are not the most important things to carry.