DIY Tip of the Day: Extended Portable Workbench. If you like your portable workbench but sometimes need a larger work surface, here’s what to do. Screw a 2x4 to a 4 x4-ft. sheet of 1/2-in. plywood, then just clamp the 2x4 onto the workbench and you’re ready to go. And since the extra work surface is fairly slim, it stores easily.