Some mammals have extra space in their cheeks so that they can collect lots of food in one go. This means they can grab more than they would be able to eat and take it home to store for another time. This is a useful trick as there could be predators around, so they need to grab whatever food they can as quickly as possible.
Most monkeys have cheek pouches, as well as some rodents. Hamsters have very large pouches that go from their mouths all the way round to their shoulders. Chipmunks are known to fill their cheeks to as much as three times the size of their heads!