One of the most popular hobbies of the baby boomer generation is stamp collecting. Many people collected stamps as it was generally a inexpensive hobby and were easily accessible through the local post office.
Stamps, used and unused have value. Never remove stamps from the original envelope before consulting a professional (Many stamps have more value on the original envelope it was mailed on than if it is soaked or pulled off). The cancellation, routing marking, and address can add value to the entire envelope.