I use a bevel and planer that I bought on Etsy. Some use a vegetable peeler which I tried but I have such unsteady hands and would take chunks out of my bars.
If I have drag marks or other surface mars I gently smooth them out with a moistened thumb immediately after cutting while they're still soft enough to smooth nicely. That eliminates the need for planing.
I bevel mine with a little carpenter's planer that I got at a hardware store. Have been using the same one, even with the same blade, for more than two years.