I believe its all about practicalities. If you are there for good old fashioned dogging fun then I have to agree with Alane. Dreses or skirts with a bit of room are ideal with the option to really set it off with heels and hosiery (a real Brucie bonus in my view!!!). Blokes I'm afraid are not going to look that good- shorts or tracksuit bottoms are best and by far the most practical- but they just look like there's no effort been put in at all!!!
Role play is totally different and if you can ensure total privacy in the great outdoors then you can wear whatever you want- just go for it!!!