Wood Grain with Epoxy Resin infill
1) Use woodfill filament, also referred to as wood infused filament. Make sure it actually has around 30% wood flakes by volume (be careful, some contain none and are just wood colored). I think I've only ever seen 30% as an option. My brands of choice are Hatchbox and AMZ3D. MG Chemicals is also good, though usually more expensive.
2) First, sand your prints down with a power tool like a dremel or a belt sander. Make sure to go with the grain of the print.
3) Use a fine grain sand block afterwards. Also consider using rubbing alcohol to remove some of that dust.
4) Stain! I use a golden oak stain and apply 3-4 layers.
5) Finish! I use glossy polyurethane to protect them and make them look great.
6) Once they're completely dry, I use UV cure epoxy resin. I mix small amounts with dyes in little cups. I use a little eye dropper to put small amounts of resin in each hole. Then I use a UV/black light to dry them in just a couple minutes. Do one side at a time until they're all done.