Definitely what kwando said about good walking shoes.

Water bottle, Airborne or Zycam type stuff, hand sanitizer, protein bars, gum/lozenges,lip balm, travel pack of kleenex all in your backpack. Ibuprofen/advil to help with the unwind in the evening/morning. Depending on your phone battery's reliability, a small rechargeable battery pack and cable might come in handy.

But I'm a chronic over-packer.

If you do some searching, there was a pretty comprehensive thread on here a few years ago, with lot's of good tips from some of our seasoned SHOT veterans.