Pipe clamp cradle
This handy under-mount rack keeps your clamps right where you need them. Simply cut a series of 1-1/4-in. diameter holes along the center line of a 2x6 and then rip the 2x6 in half to create the half-circle slots. Next, screw 1x4 sides and top to the cradle and screw it to the bottom of your workbench.
Simple Pipe clamp holder
Store bar and pipe clamps right under your workbench where they'll always be close at hand. Just screw sections of 4-in.-diameter PVC pipe under your workbench and slide the clamps into the pipe.