Each soldier can use one weapon, depending on class, and equip one backpack, which offers a bonus to some area of the soldier's stats.
The exception is William Carter, who can equip any TWO weapons, one type of Grenade, one pack, and the Van Brace for Melee attacks.
The standard backpack is given by default. Additional packs are availible to use after either unlocking them through Dispatch Missions, or locating Backpack Schematics. These schematics are scattered throughout the levels, about one in each mission, and resemble flat blue PDAs, either at blatant locations along your way, or hidden in dead-ends. They glow while in Battle Focus, so take a look if you find yourself on a "wrong turn"-- and watch out for a small ambush on your way back.
Standard Pack: no bonuses.
Sharpshooter Pack: bonus damage to head shots.
Gunner Pack: damage reduction, increases size of ammo capacity-- by different amounts to each weapon, but roughly +1/3rd to both clip and carry capacity.
Armor Piercer Pack: damage bonus to armored enemies.
Medical Pack: slows bleed-out time for incapacitated Agents before death.
Guardian Pack: damage reduction.
Stabilization Assistance Pack: significantly increases weapon accuracy.
Tactician Pack: Attack bonus, damage reduction, increases ability range when applicable.
Shield Disruptor Pack: damage bonus to shielded enemies.
Blast Protection Pack: signifcantly reduces damage from explosions and grenades.
Point Blank Pack: damage bonus to attacks done at close range.
Kinetic Acceleration Pack: damage bonus to enemies without shields.
Tactical Focus Pack: reduces recharge time for abilities, reduces weapon accuracy.
Range Enhancer Pack: Signficantly increases range of all abilities (roughly X2 of Tactician Pack).
Reaper Pack: damage bonus to enemies with low health.
Quick Charge Pack: reduces recharge time for abilities.
Rupture Pack: damage bonus to shields AND armor.
Anti-personnel Pack: damage bonus to unarmore/unshielded targets.
Laser Efficiency Pack: x2 to clip size for Laser weapons.
Endurance Pack: Increases maximum health. When revived, the wearer also recovers additional health.
Health Converter Pack: reduces health, significantly reduces ability recharge time.
Corrosive Plasma Pack: damage bonus of Plasma weapons to mechanical enemies.