I'm spending part of today preparing masonite panels for a painting-a-day series I'll be doing next month right here, every day in May. I took one large masonite panel, which can be found at most local hardware stores, and cut it down to size---I came up with thirty 5x7" panels and eighteen 8x10" panels and one or two 18x24" panels. Preparing masonite for acrylic or oil painting is simple enough---cut to size, apply one or two coats of acrylic gesso and perhaps give it a quick once over with sandpaper between coats. I'll be coating both sides of the panels and I try to get the edges as well, though that's not necessary.
Don't forget to check back next month for my painting-a-day series, and follow me on twitter---@wessf---to get updates on future posts on my website and on my life. Happy painting!