For the bench seat, purchase a wood plank, 2 inches thick, 6 inches wide, and 4 to 6 feet long. You can get these from most hardware stores, such as this pine lumber that is available from Lowe's ...

Finish the top of the bench with your salvaged banister railing. Paint it if you want a decorative bench for your entryway or mudroom, or leave as is for some rustic décor.