For Christmas my in-laws gave me a Kreg Mobile Project Center (https://www.kregtool.com/store/c64/work-supports/p419/mobile-project-center/) which has lots of holes for Bench Dogs (and came with four generic ones) and a few screws with T-nuts for adding, "a 2x4 cutting surface using the included hardware."
Where the heck do you put those two screws and T-nuts?!? It's not like it has a storage drawer or any other place that would hold screws or anything else for that matter (when the unit is folded flat). So I came up with this solution!
It's a Bench Dog (yes, it'll work just fine for that!) that has a storage compartment inside where you can put those two screws and T-nuts. I've also included the .scad so you can customize it! Want to make an extra long version that holds longer screws, nails, or drill bits? No problem! Just use the .scad.
Of course, it also fits into any 3/4-inch (~19mm) sized holes. You can see in the attached pictures that it also fits just fine in the Bench Dog holes in my Sjöbergs workbench.
Note: If it doesn't screw on very well ("grindy") just screw it and unscrew it a few times. That'll smooth out the threads and make it easier to screw/unscrew.
3D Mars PLA
I recommend printing this with max .3mm layer height (so the threads aren't too grindy) and 4+ perimeters (for strength). The hexagonal shape should ensure that much of the load (when clamping) gets distributed on to the perimeters more than the infill and should be slightly stronger than just a square or circular shape (from a 3D printing perspective).
If you really want it to be strong print it with a larger diameter nozzle (e.g. 0.6mm) in something like Polycarbonate using 100% solid infill. Polycarbonate and 100% infill would be overkill IMHO (how hard do you need to clamp stuff‽) but a larger nozzle with more perimeters should make it usable for serious/normal Bench Dog work.
Print loads of them (~$0.30 of filament)! It'll work just as well as a normal (3D printed) bench dog while also acting as a storage space. The load is almost entirely on the cap (hexagonal portion)... The tube part doesn't need to be strong since the threaded portion of the cap fits into it making it effectively a totally solid object (depending on the infill of the cap).
I used the OpenSCAD threads library (http://dkprojects.net/openscad-threads/) and typed up a quick prototype in about 30 minutes. After the first print I made a few adjustments and the second print ended up great!