This is probibly a no-brainer for anyone who has built at least one model.
I use a variety of wood chunks in various shapes and adhere course sandpaper to them for sanding blocks.
I have T-Bar sanders that are long and narrow, short and wide and all sizes in between.
A variety of dowel rods about 6" - 8" long wrapped with 60 grit. I use medium - thick CA to stick the sandpaper on adding a bead every 1/4" or so as I roll the dowel.
I used an exacto sanding block as a template and made 4 more. I use different grits on each...
One of my favorites is a 1" X 1" X 6" block of pine with different grits glued to each of the 4 sides. It lays on my bench always!
I use 3M spray adhesive to tack the sandpaper strips to the blocks. Theyre easily pealed off and replaced.
Other than the exacto block, I've never purchased a sanding block...