What about old west as an outlaw? Or if you have a side-saddle, how about Victorian or Old Irish with the flowing cape trimmed with fur? ... oh, but it might be getting too warm down there for that kind of costume. Ok -- what about a playboy bunny :LOL:
How about some beach bums? You could get into a swimsuit and use a beach towel under you instead of a saddle (maybe use a surcingle to attach it?), some of those kiddie floaties on your horses front legs, you could carry an umbrella (get your horse used to it and scare the others when you are there hahaha), put some coloured zinc on your noses, some of those HUGE sunglasses for your horse, maybe paint some beachy things onto your horses rump like surfboards, waves etc?
A race car driver and car. Maybe a Ferrari, cause of the stallion symbol they use? Get a red sheet to over your horse, make some cardboard wheels to attach near the legs, you can hold a steering wheel and dress like a car driver?
Oh my gosh! So many good ideas!!! I'm just going to have to go as a prissy cowgirl in a flowing dress who is driving a red ferrari along the beach!!! Lol keep the ideas coming! I love hearing them all!!