I was short a couple of light-duty spring clamps one evening after the stores had closed. So I came up with this simple design to quickly make some of my own. All you have to do is wrap rubber bands around the jaws to provide the clamping pressure. By varying the number of rubber bands, you can adjust the pressure to suit the job.
Starting with the pattern that you see here, lay out and cut the two clamp parts. Almost any wood you have laying around will work, but I used plywood for its strength. Ease the edges and sand the pivot contact surfaces for a comfortable grip and smooth operation.