One of my kilts is a little too long, and I've noticed that this can even happen with that kilt if I'm not careful. Like Miah, I've noticed that a good smoothing of the pleats as you sit can be a really good thing. If your wedding tackle is hanging out, notice the back of the kilt while sitting. There's ususally a good 6" of fabric bunched up right behind your butt. If you sweep it down, it'll help cover what you need covered.

I think Blu coined the phrase "butt sweep" when sitting. Just smooth the pleats and kind of hold them down while you sit. It helps tremendously.

Just as a warning, watch out for those cold, hard, plastic benches at fast food places. Brrr!