Okay.
First of all these kits could be picked up by finding them in the map.
The kit should be something like in L4D. When you pick it up from the ground, you can only use it once and it
gives 30 health(like the regular kit in zs).
Ammo: You can carry only one at a time.
Model: ofc the hl2 healthkit
You would be able to drop it just like any other weapon in zs,
You could heal others and youre self,
To prevent accidental heal you should make that the healing process would be 5 seconds or such.
This is my idea