Your game is amazing and the code is well written
It would be great if you started working on the following features
1- matchmaking system where 4 teams of 4 players can join the map
- then after killing zombies, collecting items, teams can kill each other and steal their items that they have collected as well
- all items should be in a temp state where it's stored on the server memory
- once a team reaches a safe zone like a bunker or a chopper then the team or player can extract successfully. and then the items should be stored in a database on the server. In a storage for this player.
2- then player can upgrade their armor, weapons or clothes from collected items.
3- players can sell these items in a simple database exchanger between players (bid system).
That's all, a simple 3 featuers if they were implemented, then your game will be more like extraction type game and amazingly more fun than it's now.