There are a few items on the market that claim to improve posture.
I prefer to think of ways to remind us how our posture should really look and feel. The infinity scarf is a quick posture tool that you probably already own and if you don't here's a quick way to whip one up.
These also make a great gift, all you need is:
approximately 20 x 60"- 80" of fabric or 3 - 4 fat quarters
knits work well or something from your stash of quilting cotton.