Funny thing...I just asked Jim Gagnon, a collector I met here, the very same question. Here's what he told me:

If you think you will continue with trading, I would suggest you purchase a half-dozen or so small ones [bubble mailers] from your local grocery store or department store (they are cheap). You should then recycle the ones you receive in trades from other chippers. With this strategy, the half-dozen mailers will last nearly forever. The bubble-mailers are pretty much protocol for mailing chips and do a terrific job protecting them. Also, when you mail the chip, it is a good idea to wrap them separately to prevent them from getting damaged by the post office or by clanging against each other.

(reprinted from an email from Jim without any permission whatsoever)