This one, I would be lost without. Pictures are pretty self explanatory, piece of plywood, secured from sliding around with a piece of sandpaper glued to the top. I use low adhesion spray glue.
Bench dog holes are good for so many things. I don't sand much that would require this set up, but I am noting it in case I do need something like this.
I use it constantly. If I need to sand a small part, I just lay it on this and it doesn't move around. Invaluable for sanding protrusions on segmented blanks. Many uses, I wouldn't be without it.