I'm a huge fan of wooden boxes. From Clementine orange boxes to vintage soda crates to wine boxes, and old tool boxes. There are many fabulous wooden boxes that can be found that are inexpensive or even free. I haunt yard sales, flea markets and second hand stores to find interesting boxes. I particularly like boxes with writing on them.
While painted boxes can be gorgeous, before you plant or buy an old painted box, it is a good idea check it for lead paint.
To determine if the paint contains lead you can buy a simple test kit at a hardware store.
Wooden boxes can last for years, but even cedar, which is considered one of the best woods for planters, can rot pretty quickly when filled with damp soil and exposed to the elements. Also, nails and any metal hardware used to make the box can also rust quickly given the level of exposure most container gardens will experience. To extend the life of boxes, I usually line them with some kind of plastic. I try to find a heavy duty plastic bag that will fit inside the box, which I trim to fit after I have filled it with potting soil. However, if I am planting edibles in the box, sometimes I skip the plastic because some plastics can leach chemicals into the soil.
I have been asked if a wooden box needs drainage holes and I would say it depends on how porous it is without them. To find this out, take a hose and fill your empty box with water.
If the water freely runs out the bottom, you are good to go. If the box fills up, I would drill some drainage holes into the bottom and a few in the sides, but make those holes close to the bottom of the box, especially if the box is going to sit on a non-porous surface like a patio or deck. Otherwise the water can back up into the box and most plants don't like having their roots sitting in water.
Choose plants suitable to the depth and size of your wooden box. For shallow boxes, choose shallow rooted plants. Succulents are a great choice for shallow boxes. Also microgreens or most salad greens will do ok in a shallow box.
After you have lined your box with plastic, fill it with potting soil and plant it like you would any container garden.
It's a good idea to elevate your box with pot feet if you are going to keep it on a painted or wooden deck or patio. The wet wood can stain or create rot on a porous surface. There are all kinds of things you can use for pot feet, depending on your taste and the size of your box. Everything from coffee mugs, to shot glasses. Just make sure it is stable and waterproof. Also make sure they are color-fast to avoid staining.