I don't know if you guys have already finalized field perks for every class but my ideas are;

Assault: Either a natural increase in magzine size or a buff in damage for every gun. Another idea is a grenade launcher with just the normal grenade AOE and damage.

Engineer: A placable turret that does that shoots bullets dealing around 50 damage every second or a placable barricade to block entries or to place cover with a 30 second cooldown.

Medic: Either a buff in health or an ability to actively heal your teamates that is stronger than a regular medkit but you have to be touching your teammate for it to work or within 1 meter.

Recon: Either a drone that can scout around an area with limited range from the user and it can shoot but only 10 damage per shot with a fire rate of about 1.5 seconds or a natural decrease in fire rate for all snipers.