Charcoal is a drainable item that can be used up to 10 times.
Charcoal is used as a source of fuel for the charcoal barbecue, campfire and antique oven. The burn time is 30 minutes of fuel with each use.
It is recommended to save charcoal until after the electricity has shut off, as until then ovens can be used instead.
Charcoal can commonly be found in wooden crates, which are most common in storage areas.
From items.txt (Project Zomboid directory/media/scripts/)
Weight = 8,
Type = Drainable,
UseWhileEquipped = FALSE,
UseDelta = 0.1,
DisplayName = Charcoal,
Icon = Charcoal,