I ditto Jane (Rabbit).....Check with the show coordinator(s).
When I coordinated the two shows I've done with AMHA, I asked our Stewards to have comfortable shoes, preferabley black or dark jeans or slacks and a button-down shirt. (No T-shirt) Hat was optional.
Don't know about your show, but I always provided refreshments for BOTH judges and Stewards.
I also made arrangements with the vendors (with coupons) for both the judges and stewards, so snacks and lunches were covered by the show.