You guys came up with a bunch of good things.
WD40 is so wonderful.
And safety pins and a sewing kit are a must.
(That stuff lives in my show trunk so I so frequently forget I have it.)
Another thing. Be sure all your stuff is clean and ready for showing.
I tend to pack everything the night before. The only thing I have to get ready in the AM is the last pouring of ice into the cooler and the horse.