Blade, light and lift..... the cellphone, keys, wallet of scuba. 

A Line cutter tool is excellent for cutting fishing line off and even steel leader off of the dive site or a diver, should you or your buddy become snagged. A1000 Lumen light with a retractor for hands free use exploration of all those nooks and crannies on the shipwrecks. 6' Surface marker buoy is something no diver should be without. When inflated these SMBs are visible from a mile away or more and required for many drift dives in other parts of the world. Additionally it has nearly 50lbs of lift and can be used for safely recovering heavy objects at depths.