I'd say pack electrolytes, feed it to him. Couple days before the show in his normal feed or water so he gets used to the smell and taste.
When I groom at over night shows, 2 nights per show, 4 shows in the summer we pack extra hay, do lots of hand walking, keep a close eye on water intake and how much poop we see each time we clean the stall.
I'm not sure in the country you are, but if it's winter like it is where I am, bring extra clothes for your boy to keep him warm and dry.
We also spray santizer on the stall walls in case any horse that was last there had any bit of anything, sounds anal and silly but never had any issues!