Ohhh yeah minis!
Off topic but the pony in your avatar picture looks identical to my pony Cocoa. She's a Shetland pony...
Anyway, the list...
Besides the obvious, here's little stuff I always always always bring to show my Shetlands.
HAIRSPRAY. Not for you, for your pony!
Many brushes (dandy, curries, body, face, hoof, etc)
Hoof pickS. You're probably going to misplace one, so bring 2 or 3.
Baby oil or showsheen. I prefer showsheen because it's easier to use.
Lots of rags and cloths.
Stuff to bathe them (including a hose if there's not one at the show grounds)
A show halter.
A stable halter so you don't get the show halter dirty.
A few lead ropes.
A fly sheet or something to keep your horse clean between classes.
A sponge or two
Whatever else you thing of!