Guild inventory is a collective amount of Cans/Crates/Brains/DNA and unit packs obtained by the guild. The leader/officers may decide how to divide this amount up.
5% of the Cans/crates/Brains/DNA you earn will be given to the guild inventory. This is 5% of your total take and the 5% that goes to the guild will not be out of your personal amount earned.
Unit packs are given to the guild inventory upon completion of raids.