The humble wooden clothing peg can be used as a handy lightweight clamping device for many jobs.  They are easy to get and cheap as well (If you are really lucky you might be able to steal them direct from mother’s clothes line).  Pegs in standard form are not as good as those that have had a spot of minor surgery to give you a bit of extra clearance (check the photo).   If you need more than the half inch or so grip clearance that is available from a single peg, you can glue 2 pegs back to back with the adjoining legs removed to make the grip clearance over an inch and a half or glue one peg to each end of a wooden block for whatever size you need.  These clamps are lightweight, provide firm pressure, and with cyano glues they can be created in seconds.

The more worldly wise among you will recognize these things as clothing pegs.

The centre one is unmodified, the other two have been converted to spring

Clamps, the single item will open out to 16mm and the double to over 40mm.