Wood handles on tools are probably the easiest to pull off because the surface area is smaller as opposed to making a table top look convincing. There are a bunch of systems out there, but really all you need is an appropriate base color and a darker shade for the grain. I keep old useless brushes that have the bristles screwed up just for wood texture, but you can cut a cheap brush so there are only as few hairs sticking out.
Paint the base color (light for sunbleached or darker for newish) and then with the dark color (heavily thinned), drag the cut brush down the length in a straight line. If your bristles are spread correctly, you'll get nice thin grain lines. Then weather by dirtying where the hands would grip it. If you really want to go crazy, you can dent the axe handle were it would contact stuff under the head. Practice on some old sprue pieces or any scrap plastic until you get a smooth brush stroke.
For the tool heads, I go the same I would with tracks, then maybe add some oil staining. Here's an old tutorial using Tamiya colors, I do the same now but with Vallejo. The pencil would be used around axe heads, etc.
http://ausfwerks.com//techniques/tracks/main.html
This one too, up to the whitewash:
http://ausfwerks.com//techniques/spare/main.html