Make a chair seat from old belts! I used as many leather belts as I got after my mom died a couple years ago and wove them onto where the seat was missing from this chair. I secured each end of the belt onto the wood with upholstery tacks.
I was in a local second hand store and saw an awesome wood framed chair; they removed the old caning that formed the seat and weaved old belts onto the seat frame for a new seat. All the belt buckles were on the bottom so all you saw was the leather part of the belt. It really looked nice and it was very sturdy.
Shoulder Straps for Purses
I've used them to make shoulder straps or purse handles for handmade bags. I also made one into a collar for my dog when his turned up missing.
Find or make some flat wood picture frames and then cover them with cut-up belts that you have mitered the edges on. It makes for a nice western look frame.
Borrow a book on macrame crafts from your local library. That's where I found macrame belts using the leftover belt hardware. Great way to recycle, and makes a good project for Boy Scouts to use their knot tying skills. The naturally formed "loops" in macrame belts hold carabiniere, flashlights, knives in knife-cases, compasses, etc.