1. killstreaks for sure. after you kill 4 mudcrabs or so azura will drop a care package near your cordinates. 7 kills gets you rc missles you can use to shoot down spy planes uhh.. i mean dragons. and 25 kills earns you a tactical nuke that defeats any enemies in the current dungeon you're in/ proximity (if you're in the country side).
2. perks. commando(farther melee range), danger close(increased explosive damage), steady aim(increaased hip fire accuracy), last stand(gives you a temporary extended life your pistol drawn) just to name a few
3. pack-a-punch. getting tired of your gun? upgrade it in a pack-a-punch machine to upgrade it's firepower! turn your ordinary pistols into grenade launching pistols!