From memory I just wore a white epaulette shirt (as I did throughout my entire training) blue pants and black boots. Some guys sucked right up and took a paper for the ATO and some even catered with cake/sandwiches etc. I didn't bother with this however.
No Bars or wings, leave that for the aeroclubs
I remember one school gave you a bar for GFPT, PPL and CPL so walking out to a 152 some students had 3 bars while they were doing instructor ratings! A bloke I knew wore 2 pairs of wings at the same time, one for gliding and one for his fixed wing stuff, he only had a PPL.
(I hope you read this struggler)
I must admit it's a little bit of a novelty when you get to don the full uniform and head to work for the first time. The novelty wears off real quick and you envy the float guys in crocs and polo shirts while you're sweating on the ramp in full uniform loading a busted arse GA machine full of freight.......
Anyway good luck with the test, don't fall for the tricks and remember to say NO if he asks you to do something against the regs.