I got tired of lugging a bag around during the really hot summer months, so I decided to do a little engineering of my own. This ended up being free since I had all of the components, but never the less it works.
Built using one of those folding golf carts, some nice water sealed wood and some hinges for the bag shelf and the cooler/milk crate shelf. Also nice having the scorecard holder, and it has to golfball holders that work well for holding towels as well. As you can see, I also added a nice mounting point for a cheap folding chair umbrella. It works to keep the bag and towels dry, and I usually have an empty milkcrate attached when I know the course needs a little litter picked up.