Suspenders go in and out of style for fashion, but in our house they never go out of style as useful tools. Between the double clipped ends, the long elastic length, and the adjustability, they are invaluable to us.
We took an inexpensive pair of suspenders and removed the metal slide that held them together in the back by clipping it with wire cutters - if the suspenders are sewn together, just pick out the stitching. Then you have two very long lengths of elastic with clips on both ends.
We used these to hold towels on the vinyl bench seat in an old station wagon instead of slipcovers, and just stretched them diagonally across the back of the bench, clipping beach towels in each corner.
After we sold that car, we then used them stretched from corner to corner underneath an air mattress to help keep the sheets from popping off the corners. We never had guests complain that the sheets came off the bed!
I just love those ideas you posted. I am a big fan of using something that is in perfectly good condition for another job around the house. You could use it across the kids room to hang pictures or art work up for them to display.
I purchased an inexpensive pair of Suspenders (braces in the U.K.) to hold the bottom sheet on my bed in place, because they actually cost less than the sheet holders that are now being sold.