Re: "bondo" for wood stock??
Screw Bondo.
The best filler is the wood itself, and the best binding agent is the finish itself.
First, steam out dents by placing a thin absorbent pad over the dent, saturated with rubbing alky, and apply a steam iron over the pad. This will steam out and reinflate the individual tubular wood fibers with the expanding steam while plasticizing (liquifying) the natural lignin wood resin. When it cools, it will be a lot more like it was prior to the dent.
Ammonia will also work but it stinks like heck. Ammonia does a much better job of plasticizing lignin. If you use it, try to find janitorial strength ammonia in a hadware store.
Keep ammonia and chlorine bleach far the hell away from each other!
When mixed, they release chlorine gas, which is deadly. I say this because I sometimes also use bleach (and fabric dye, for that matter) on stocks. I make damned sure the ammonia gets used first and has thoroughly evaporated before I reach for the bleach. Ammonia first, because bleach leaves chemically active residue, but ammonia is a gas and doesn't (I hope).
Next, using a medium grit sandpaper (between 320 and 180), put down a glob of finish material (I use Birchwood Casey Tru-Oil because it's repairable and has a long working time) directly atop the blemish and begin circular wet sanding it with the finish agent. A 'mud' will form, and this is your ideal filler.
Keep adding finish agent and sanding until a puddle of filler/mud covers the blemish. Once the covering is substantial and uniform, put it all away in a warm, dry, dark place and leave it completely alone for at least a week.
It will have completely hardened. If it hasn't (a gentle thumbnail leaves a dent) give it more time and apply a thinner layer next time. Sand it down to the grain and see how well you've done. If you need more fill, repeat the process.
When sanding near sharp edges, employ a rigid sanding block so the edges don't get eroded.
If the ding is so extensive it won't steam out and it won't fill, put wood filler down into it, then remove enough to leave a shallow depression which can be filled with the above technique. Not deep, we're only talking about the thickness of a few layers of paint.
This will provide a repair that's worthy of being seen through a transparent finish.
Greg