Legs some think plain is always good, simple trousers will do, that aren't obliously jeans, again this can be bought specifically for the events or not here are a few examples
All these links are form the http://www.lrpstore.com/contents.asp but here are other places to go, some cheaper some more expensive and many that are less generic
Glic
i thik kinda generic black combats and a black LRP shirt are the best basic, cos you can pretty much stick anything over them and all people will notice is the kit not the basics. Also they don't show beer stains
Gward'ogan Miradomas
There will also be a freecycle stall at this event also, so a good place to pick up a new/costume if needed.