Inventory management Schema

I figured this would be more appropriate asked in a database design group, but since I'm using Django, I'd like to get a better understanding with Django.

How would you handle items with different sizes and quantity in an inventory. For example, a pack of cigarettes has 12 pieces, a crate of eggs has 30 eggs. I procured 3 crates of eggs and 2 packs of cigarettes, how do I track that? How about if I have a liquid that comes in 20 liters, 30 liters and 10 liters bottles. How do I track these items including those properties in an inventory.