I have never been to a frag swap. If I go do I have to bring frags to trade or can I just purchase?
For the most part unless you arrange to "swap" with someone before the show there is not much "trading" going on so much a bunch of vendors or hobbyists with tables selling frags. I am sure there are exceptions, but think it more of an older term and is probably more accurately described as a "frag sale" now.
So short answer is no you dont have to bring anything to the swaps.