If melee weapons can be coded to consume ammo per strike you could make a melee mod for cutting/stabbing weapons that adds X charges of poison.
Crafting venomous darts/arrows/bolts out of wasp/bee stings
Fungal grenades as both a craftable (Tin can + fungal corpse) and mutation/monster attack.
Crafting a manhack into a battery gobbling boomerang
Fungal ‘armor’ plating a vehicle if you park it too long in a fungal zone. Not a good thing if you don’t love fungus
Handcrafting shoddy ammo for the various RPGs out of duct-tape, firecrackers and military grade explosives. (Landmines/dynamite)
Being able to use a sling to throw grenades further.
The ability to attach jumper cables to a battery and a wire/barbed wire fence, metal doors or bodies of water to electrocute anything that smashes or tries to open/climb it.