there should be an extra slot where after you choose your weapon you can choose one of the 6 support items
1: HMG it can be placed on any block it takes up 1 block in size
press e on it to use it and you will control the gun it works like an smg with an 80 round magazine and 1 extra mag
2 Mortar when placed it has a 50 block range and an explosion similar to a grenade you can fire it blind or if you have another person with you who also pressed e on the mortar you can press m to target an area
and fire there it has 10 mortar shells
3 Medicine box heals people near it slowly
4 ammo box ^ same as above except with ammo
5: Pistol a backup weapon with 8 rounds and 24 in reserve
6 Revolver 5 rounds slower firing than pistol 10 in reserve as powerful as a shotgun in some cases
sorry for my poor english