The best art supply, that isn’t an art supply is the Rapseco Supaclip 40. Why is that? ‘Cause it’s a binder clip but without those little arms that get in the way. Those arms can be nice, and yeah you can pinch them and take them off if they are in your way, but I lose them when I do that. So I don’t have to fold them down and have them cover the paper I want to clip to a panel and I don’t have to fold them back and have them hang off the edges getting in my way. I can just use Supaclips.
That means I can clip paper to a panel and use it in anything that is built to hold a panel, like a pochade box. And they add just a hair of a sand-off so I can stack painted panels. I freaking love Rapesco Supaclips. The size 40 are perfect for eighth inch panels.