Rampage is a gear perk that stops your gun using ammo for a while after takedown and melee kills. Any weapon with more than one round in the magazine qualifies, so it rewards mixing melee with gunfire.
Kill an enemy with a takedown or melee hit and your next shots do not drain the magazine for a short time. You can follow a takedown with a burst at the next guard and lose nothing.
Wear Danny's Button-Down in the chest slot. Gear perks are fixed to the piece of clothing that carries them, so you get this one by wearing that piece, not by unlocking it in a menu.
Strong for aggressive close-range play. It also pairs well with the Gladiador Supremo, which lets you do machete kills on any enemy in open combat.