Sights, scopes, perhaps even the occaisional underslung G/L? On the otherhand, there is the danger of overclutter, perhaps only 2-3 of those guys should get the goodies as upgrades.
TI/IINF should be assumed integrated into the helmets, as with TACCOM, but is one of them carrying the squad Comms gear?
The radio backpack from the Einherjahr is a good option (which has found its way into the Damned offerings). The one off the Grognards command sprue is too big for squad use IMHO.
I note the metal RPGs on 2 of the figures, where did you source these from?