Sarge's idea is pretty good. But... I say he should be special.
Ammo Carrier: As Sarge stated, moves somewhat fast, tad bit more health, and has extra ammo. But this makes only for light weapons, I.E. rifles. One Grenade perhaps?
=EDIT=
Idea for the Medic I stated, his Medkit.
The process is as follows:
Equip the Medkit Box
Aim at the wounded soldier.
The medic will proceed to kneel down and open the box, pull out a syringe or something and heal the soldier.