One 1"x4" (the length will depend on how many you want to make, but you will need at least 2 feet to make one holder)
Sand paper, in various coarseness.
4 oz. canning jars. I have only seen these sold in twelve packs, but they are useful for so many things.
A saw. A hand saw would work, but a chop saw gets it done fast.
An electric drill.
A 2 1/2" hole drill attachment like the one seen in the picture.
Nice, but not necessary, is a palm sander, or any kind of electric sander.
So here's what to do after you've got all your supplies. Cut two 11 1/2 " lengths. On one of them, mark three spots to drill your holes. Make a mark in the exact center, and then measure out from there. On mine I measured 3 1/2 " away from the center on both sides. Remember a 1"x 4" is not 4 inches wide. They are usually 3 1/2", but measure yours to be sure.
Put a scrap piece of wood under your board, then clamp it down. Drill your holes.
Now, glue the two boards together, matching them up carefully and clamping.
Put your jars in, and that's it!