I remixed Jmadden99's Toilet Paper Tube Caps to remove the hooks. I kept breaking off the hooks or having the bands come off the hooks while filling. I also removed the grooves, because they never printed cleanly on my printer.
I may play around with the size of the holes a bit. I'd like them to be able to pass a rubber band through without having to poke it through with a pin, while not having any extra space.