I needed a couple wood bungs when building my Wee Lassie II, but I didn't have a plug cutter. Even if I did, I didn't have a drill press to use it in (and I couldn't justify the cost of a plug cutter and drill press for 2 bungs. Almost, but not quite). I would have bought a bag of bungs from the local woodworker's supply, but they didn't have any with the diameter I needed. So, I used this simple method to make them pretty easily. If you only need a few, this technique works great.
First, rough-cut a disk of wood for the bung. I used some 1/4" thick Walnut and cut it roughly to size with a Japanese pullsaw. Then cut a 2" length of 3/8" dowel. If you can, cut it in a miterbox to ensure that the end is perfectly perpendicular. Glue the dowel to the center of the disk. Simply put a generous drop of glue on the end of the dowel and stand it on end on the disk (I used Titebond II).
When the glue is dry, chuck the dowel in a hand drill and clamp the drill to your workbench. Lock the drill on and use some 80-grit paper attached to a rigid backing (a scrap piece of hardwood works great) to slowly shape the disk. Don't use a soft sanding pad or you'll end up rounding the edges of the bung. Also, don't push too hard, just let the sandpaper take off the corners. To make a tapered bung, hold the sanding strip at a slight angle and make the taper towards the outside. Stop the drill occasionally to check the fit of the bung in the hole of a sample block. After you've got the bung shaped to your liking, you should be able to just break-off the dowel at the glue joint (it happened to me by accident). If not, just saw it off. Presto, custom-size bung. Not as quick as a plug cutter, but it works in a pinch.
-Ross