Aside from the obvious things in a bag (balls, tees, gloves, range-finder, etc), here are the top 10 "must haves" that everyone should keep:
1) neoprene koozies
2) extra 9V batteries for the Bushnell
4) benadryl & ibuprophin
9) $20 or blank check (in case you leave your wallet in the truck or have no cash for side-bets/beer cart)
10) business cards (if that appys to...