zpacks.com can custom make you either a silnylon or cuben fiber stuff sack for your NeoAir, I got a medium NeoAir and find it easier to only fold lengthwise in half (not in thirds) for refolding, so if I got a NeoAir stuff sack, I'd have to refold in thirds. I ordered a custom sized stuff sack made of cuben fiber from zpacks.com to fit my NeoAir. Contact Joe at zpacks.com.
I thought about a rubber band but worried about the nipple of the pad. The stuff sack will help protect that nipple plus the fabric itself and the weight will only be a tiny fraction of an ounce.