This is my first year seed trading, and I ordered and bought little coin envelopes for a large group swap. But then I received seeds in folded paper envelopes from one trade. As soon as I ran out of the seed packets (which didn't take long), I started folding my own. Using garden catalogs is my favorite--only thing is making sure to fold it so the back has a space where you can clearly label the seeds. They can be reused a couple of times, too.
I do like the idea of sharing them, too--I've kept old gardening catalogs for years, reading them over and over, before coming to my senses and throwing them into the recycling bin. But probably someone else would have liked to read them!