It all depends on what you will be doing with the case? Range? Bug Out? Truck Guns?
A case like that is looking good for a grab and go....if this is the case, a rifle, eight 30round mags, handgun with at least 6 mags, batteries for any electronic optics, gloves, FA kit, charger cords for the cell phone, snacks and bottle of water....just off the top of my head.
If a range case, add ear pro, eye pro, targets, stapler, duct tape
Bronc