Queen of Baby Gadgets: SippiGrip

Our oldest daughter has definitely inherited her mother's clumsiness, and with said clumsiness has come many dropped sippy cups! At first it was so frustrating, but then we purchased BooGinHead Sippigrips. They cost less than $6 at a local baby store. (Our girls wwouldn't take them, but you can buy matching pacistraps too.)
This is a product that I give a thousand thumbs up. If you sew you could probably make a similar product very easily. It's simply a strap, one end straps with velcro to the high chair, stroller, car seat or whatever, and the other straps around the cup itself. (It has a grippy material on the back side which helps it to hold to the cup.)
I now own three of them. I keep one in the diaper bag, one on the high chair and one in a drawer for when I'm washing one of the others.
Great product and totally worth the price!