realistic wooden boxes

I always use real wood....
I use balsa and some string for side handles. I then prime the box black, shoot on the topcoat color while allowing the black to show through slightly, then wash and drybrush. The wash and drybrush really picks up the detail in the grain.

Gip Winecoff

I haven't tried using real wood, but it sounds like it would be a good idea.
I generally basecoat the plastic in a lighter brown tone, then several washes follow. Once dry, a drybrush with varying shades creates a more realistic overall finish.

QUOTE: I use balsa and some string for side handles. I then prime the box black, shoot on the topcoat color while allowing the black to show through slightly, then wash and drybrush. The wash and drybrush really picks up the detail in the grain.

Seems redundant to use wood and then paint it . . .so it will look like wood.

You might try basswood (usually sold next to the balsa in your LHS). It has a tighter grain that looks more to scale than balsa. I generally subscribe to the old model railroad adage that nothing looks like wood like wood does.

If you use plastic: Scratch some woodgrain in with a needle. Paint it the overall base color of the wood. Enhance the woodgrain with a watercolor pencil, chalk pastel pencil, or dry brushing of the correct color. Seal with a clear flat coat that won't attack the base color.

I did the deck of a ship with MM enamel color "Wood". I used a black watercolor pencil for the wood grain. The last step was to dry brush over the watercolor pencil with enamel tan. It made the black pencil marks blend and lighten up. Plus, it added one more dimension of wood/tan color to the blend.