Bring water, as it is can be hot. Bring a sweatshirt, as it may be cold. Rain suit and rubbers as it may be raining. A C-clamp to hold your gunbox open, as it may be windy. A cart to carry everything.
Some people bring a bungee cord to keep the gunbox on the bench during heavy winds.
Only give the competitor who is scoring you the score sheets for that day, as they may not be there the next day. Wooden or brass rod. Spare parts I take it back. You don't need a gun box. You need a pickup truck to carry all this stuff around.