I start off with at least $100. Roll of quarters, and the rest in ones and fives. We live out further and to send someone after change is not easy on a Saturday. I'd much rather have to much then not enough. The reason I only have one's and five's is I can always give someone 2 fives for change but if they only need 1 five and I only have a ten I'm sunk.
I start off with $100. Lots of ones & fives! Few tens! And $10 in coins! I have a lock box that opens with a key & has all the different compartments for money. I always use a bike lock to attach the handle of the box to the pole my table sits by. Carry the key in your pocket. People see you talking with someone & you'd be surprised how many are tempted to go for the box