What I mean by that is what kind of perks are you unable to play without? For me, it's Stalker, Ready-Up, and Sitrep. Sometimes I'll slap on Dead Silence if I run into Amplify campers.
The reason for Stalker is because I like constant movement, even while ADS'ing. If I don't have stalker enabled, I end up being a slow moving target for someone to shoot at. Stalker is especially good for firing my shotgun, pumping while taking cover, and popping out of cover to fire again.
Ready-Up is there to help me react to an enemy combatant. Without it, I'll end up losing more gunfights.
As for Sitrep, it's not only for avoiding pesky IEDs, but I can also track down enemy streaks and destroy them for extra points (or use a ground jammer). But the perk is mostly there to avoid IEDs since they're so powerful (especially after two nerfs).
Dead Silence is quintessential. It's like the Black Ops II Flak Jacket. You don't want to get C4+Scavenger abused? You ran Flak Jacket. You don't want to get soundwhored and give your opponent the 98/2 advantage in the 'gunfight' (Pre fire-fight)? You run Dead Silence.
Hardline for me is extremely useful because I only run Assault and it's necessary to confidently hit streaks above the Guard Dog. It's an underrated game changing perk. Being buzzkilled 1 off a Helo without Hardline is the difference between a win and a loss.
No other perks I would consider mandatory though. Possibly a Marathon-Dead Silence-Agility trio for Vector gameplay. Deadeye is powerful in the right hands and Recon is very useful with Thermobarics and other explosives combined with +1 Tac and +1 Lethal.