A bench hook is a handy tool whenever you need to chisel/plane/checker etc. a flattish workpiece. Hook the hook over the front edge of the bench, push the workpiece against the stops attached to the hook plate and you've got something to resist the force generated by the tool when you use it on the work.
I have a large one made of 3/4" plywood that I use often on my workbench in Garaj Mahal, my shop. It's so useful that I wanted a smaller one to use on the worktable that sits next to my desk. This first picture shows what I built...
The large stops at the end of the plate are permanently screwed to the plate and can resist quite a bit of force. For smaller workpieces these stops are too far away for comfortable work so a repositionable stop was made. It's held in place by two bolts that can be located in a set of holes in the plate to provide three different positions for the stop. These holes and bolts can also be used to secure work with clamps as shown by the sample setup in foreground. Obviously, as need arises, more holes can be drilled in the plate to accommodate other clamping options.
A view of the bottom of the plate showing the hook and the countersunk holes for the bolts. Countersinking allows the plate to lie flat on the worktable.