I've recently been on one with a Dukes of Hazard/Cowgirls theme - was nice and easy to do as lots of stuff around on the High St at the mo and it was quite adaptable - dependnig on what you feel comfortable wearing (we had two pregnant ladies who dressed up!). On that night out, we also saw a group of Hens dressed as Where's Wally, a group of bumble bees, fairies, Vikings (!), 60s/70s - that's all I can remember - was lots of Hen groups in York that night! I'm going for a posh frocks night - with red wigs (I'm a red head!).