[JesseK]

All of his coach buttons from every competition he's ever coached for good luck

Or maybe just some bottled water for the drivers since there's sometimes not a good spot on the cart for it

Or perhaps some emergency tools -- #10 bolt tools, zip ties, etc -- for the "oh crap we didn't do X" moments you experience when you set the bot down on the field, realizing something's loose, dangling, or otherwise about to ruin your match

(I've never seen inside, but this is what would be in my backpack if I had one)