Rubber bands are great (as long as they're nowhere near a child's mouth!!!).
We used rubber bands for early child-proofing to keep Karston out of cabinets, and they worked well. Of course, now he puts the rubber bands back on if you leave them loose, but he also no longer tries to get into everything. The rubber bands worked until he learned what not to do. Now that he's older, he knows his toys and they're more fun anyway.
I'm using a rubber band on my wrist to keep track of which side is next for breastfeeding. I'm faster on the setup when I don't have to think, test, or remember which side Cale gets. Very handy, especially at night! I sometimes wear a pretty stretchy bracelet during the day, but at night the lowly rubber band is much more comfortable for sleep.