Most pet shops sell dried food mixes specifically designed for hamsters. These usually consist of crushed oats, barley, rodent pellets, peanuts, sunflower seeds, maize, dog biscuit and some of the better hamster mixes provide a wider variety with the addition of ingredients such as dried fruit and vegetables.
There are also rodent or hamster pellets sold in some stores. These are compressed food pellets and although they are designed to meet a hamster's nutritional requirements they do not give the hamster any variety and some hamster mix fed with the pellets provides an adequate main diet with some variety.
Food mixes designed for other animals should not be given as these may not be suitable to meet your hamster's dietary requirements. However, a small seed bird mix can be added, particularly for dwarf hamsters or hamsters with young babies.
Hamster mix does not perish quickly and so may be stored for some time in dry conditions without problem.
Any changes in a hamster's diet, even changing to a different hamster mix, should be made gradually as a sudden change in diet can cause your hamster to become ill.
Hamsters should be fed a basic hamster mix and this should form the main part of their diet although other foods can be given as treats.