Consumables are anything that can be purchased and used. They are only for one tank at a time, though you can buy the same consumable and use it on multiple tanks.
Consumables are typically things like extra fuel upgrades, like 10% and 15% Octane Gasoline. There is also the Repair Kits, Large and Small. Large is used to repair the entire tank and every unit, provided you're still alive. Small repairs one module.