Consumable XP
I try to encourage things that benefit everyone in the game. The guys bring chips, candies, waters, etc to add to a chest I keep in the game room that we call the "Treasure Chest". Every item dontated provides what I call Consumable XP that is awarded to the party. This xp pool can be used for anything the group chooses. Its not a great ammount at any one time, but over months of gaming it builds up. It levels off PC's who are really close, and it's been used to pay for magical item creation. Its been a very useful (and delicious) idea that has served us well since we started it about six years ago.