Possible an M4Super90
But i guess taking your chance at a hisec key wouldn't bother.
If you're close to ranking up probably a XP + GP Pass wouldn't hurt, 100% XP + GP Passes are the best common things to find in a Hisec, but you can only get the 30% ones ( correct me if i'm wrong, haven't bought NX in months ) in the Black Market.
M4Super90 would be hella' good if you love small maps. if you're not a sniper, then prolly get these:
-XP/GP Pass or a hisec Key
-99nx grenade pack if you need it, if you can buy it with GP then nvm.
-Cyclops Bandana for speed
-M4Super90 for massive accolades
-Mp7 Mod for spraying in CQC but like you said, you have the M4A1 CQB so nvm.