A couple of sawhorses and a sheet of plywood make a handy table, but if you put too much weight on the middle, it’ll start to sag. Rockler has come up with some brackets that slip over the saw horses and hold another 2×4 or two for supporting the middle of the table.
Rockler also includes screws for securing the brackets to the sawhorses, which’ll probably get lost anyway. I don’t see why some general purpose constructions screws wouldn’t work just as well.
A four-pack of steel brackets runs around $13.
Saw Horse Supports [Rockler]