The Side Pocket Foxtrot is a relatively large pocket that is fully enclosed by a zipper. It also has a single pen slot on each side, and a flat slip pocket on the front cover. This pocket will be great for holding larger items that you don't want to fall out if the entire bag is tipped, or goes on its side, or even goes upside down. NOTE: This side pocket will not mount on the CS2 or CS3 because these center sections do not have FLEX Mount Side Pocket Stations. Only the CS4, CS5, and CS11 can accept Side Pockets.