I always like to be a supportive team mate.
I thought maybe have a skill that allows your bullets to convert to health when you shoot a teammate and you can't do it to yourself. Obviously have it low so its not op, but I often see low level players dying all the time and I'd like to help more, and with how the game is its basically just mindlessly killing zombies which is great but something more would be nice. Or maybe have a skill that allows you to give med kits, or possibly a perk you can activate that can heal others.

Always nice to have more co-op stuff but with how the game is its less co-op and more basically I am just in the same game as others.