Any one of them would have been an excellent place to start learning how to refinish a stock, and/or apply some checkering, or maybe do some recheckering.
The first of these is a single-line cutting tool, which you use to lay out two master lines on each panel of new checkering.
Once you have the lines all spaced out and deepened somewhat you'll switch to the single-line cutter to deepen the grooves to the proper depth, which means bringing the checkering diamonds to a point, but no deeper.
If you have long checkering lines on a relatively flat surface you might want a longer single-line cutter, which acts much like a big block plane or jointer plane in that its length helps you keep the lines straight.
The full-view single-line cutting tool that I use to deepen my checkering and for recutting older checkering is a loop of steel wire with the cutter suspended in front, so you can see what you're doing a bit more easily.
Never allow a checkering cutter to even touch another tool or metal object.
Some time back I recut the checkering on an old Browning Citori and actually ran into several large grains of sand that had been pressed into the wood when the previous owner probably fell or dropped the gun in the dirt.
The first thing I would advise any would-be checkerer is to read the Bible of this endeavor, Checkering and Carving of Gunstocks by Monty Kennedy.
One can also be purchased from some of the manufacturers of checkering tools.
Speaking of tools, there are three major producers of checkering tools: Dem-Bart, Gunline, and Brownells.
This is important since the checkering is done in three steps, each step deepening the line until it is just right.
Look at some of the factory checkering that is being done now.
One of the elements in the kit is a professionally produced "how-to" DVD that guides the student through the checkering layout, line spacing, line deepening, cross hatching, bordering, and finishing.
With the exception of a few odds and ends you already have in your shop (and a checkering cradle which you won't need until after you've graduated from wooden coasters to guns), everything else you'll need is packed in the kit.
After about 30 hours of practice, patience, and persistence working on both sides of the coasters, you'll feel pretty confident about taking on a real checkering job.