Agent 47’s briefcase can help him smuggle items into areas where he shouldn’t. It allows him to conceal weapons that might otherwise draw attention and blow his cover. Once the briefcase is unlocked, you can use it on any level by equipping it during the planning phase of a mission.
At the Mission Briefing Screen just head to one of your Gear slots and select the briefcase to equip it. Once you do, you will be given an extra inventory slot which you can use to conceal a weapon or item.
Agent 47 can walk around with the briefcase, he can hide the briefcase and return to it, or he can get creative with the item and throw it over fences or strategically place the item all over any map. The briefcase can be thrown just like any other item in the game by pressing the L2/LT button while carrying it and then throwing it with the R1/RT button. It’s important to note that you can have multiple items in your hands when carrying the briefcase. If you have another item in your off-hand you will not be able to throw the briefcase. You must press up on the d-pad to put away the secondary item to throw the briefcase.
To retrieve items from the briefcase that you’ve smuggled into an area, simply drop the briefcase by pressing down on the d-pad and then pressing Square/X to retrieve the concealed item. The briefcase is extremely helpful in smuggling in things like Sniper Rifles as walking around with a massive rifle on your back is a way to draw attention to yourself rather quickly.
The briefcase does allow you to get creative. You can smuggle anything in the briefcase, from guns you have unlocked, to distractions, melee weapons, tools, poisons, and explosives.