Sometimes wrongly referred to as simply "machine gun," the submachine gun (or SMG) is an automatic weapon that is designed to fire pistol cartridges. Such a weapon is highly useful in a zombie apocalypse situation due to the fact that it combines the automatic firing capabilities of a machine gun with the cartridge capacity of a pistol. This is a great space-saving feature. Simply make sure the bullets in your pistol are of the same variety as your SMG, and you've got that much less equipment to carry.

Tip: For even more portability, consider a machine pistol. They have an even smaller form factor than an SMG while retaining the automatic fire capability we all know and love.