This is one of the easiest things I've ever made. You most likely have everything to make it laying around the house except the old wood. I just happened to have an old crate I was getting rid of that I tore this piece of wood from.
These are the rest of the things you'll need. A paint brush to paint the wood with, some white paint, something to mix the paint and some water in, a pencil and a fine paintbrush.
Mix up some whitewash to brush over your wood till you are happy with the color.
You can either stencil the letters on or draw them. I chose to draw them because I didn't have any type of stencil that would work. I then painted over the pencil with white acrylic paint a few times till it showed up nicely.