I also use a piece of plate glass to cut on. It used to be a table top in my 5th wheel that I had special cut while we were on the road. If you have access to old car windows, some of them work real well. Some of the old pickups had flat rear windows and they also work well. The car / pickup windows work well because they don't break easy and in most cases don't shatter if you mess up.

Another cheap hint : with most X acto knives the handle is round and that makes it easy to roll off your table. Take a small piece of tape and wrap it around the handle leaving a small tape tab sticking out the side. The tab will keep the knife from rolling. If you want to spend some money, you can buy a small foam sleeve at Wally world that fits over a pencil and sort of does the same thing. I'm cheap and use the tape.
ENJOY !!! RED