Money is useful, especially if you wish to eat or drink, and didn't bring your own food and beverage, or didn't bring enough to last you, or you eventually decide to go home, and need more gas, or you want to buy performers' CDs or tapes.

But I was thinking of things like:

A flashlight, for the long three a. m. trek to the johns.

Another flashlight, to use to find the first flashlight in a dark tent.

A travel clock with an illuminated dial, so you can yell "Stop banging on that goddam banjo, don't you know it's three in the morning?" and be accurate.

Et cetera....

Peter.