Piggyback, $70, US shipping included
 
The Piggyback is a great multi-purpose way to add 700 cubic inches.  Attach it to a frame for use as a small day pack.  Set it on the meat shelf between a frame and main back.  Use it as a panel outside the main bag.  Two compression straps hold everything together, and two bottom straps can attach to various strap configurations on the bottoms of main bags or frames.  Two flat pockets inside help with organization, and a short, flat pocket on the back can hold a gun butt when you strap your gun outside of the main bag for long hikes.
Compatible with Kifaru frames, Mystery Ranch Guide Light frames, and MOLLE-equipped panels.  Please specify which system you intend to use as buckle configuration may vary between them.
 
10”x 4”x 18” (700 cubic inches/115L)
12 oz.