Simple items

I'd have the weapons icons replaced by the shots they do. Like for example Electro could be a thick beam with a roundish head going diagonally up from bottom right to top left, and two or three balls beside it bottom left. Crylink could be three particles with spread movement indicated by three lines coming from a spot bottom right of the icon and expanding towards top left corner. Hagar coul be three little rockets travelling parallel with trails. Mortar would of course need an arch trail in some way, Nex could be just a glowing beam, Rocket launcher would be obviously a (flying) rocket, maybe with a short trail but the rocket would need to be bigger. I tried to put some of my ideas into a graphical concept, but I discovered my limits rather immediately.

The health items seem just fine for me, though maybe they could orientate themselves more towards the Xonotic items rather than Nexuiz items?

You could also indicate "weapon" pickups by a frame around the icon and "ammo" pickups by no frame, to make the difference immediately visible.