Most of the time, your passport or driver’s license will be enough to verify your age. Other forms of identification that may do the trick are a wallet copy of your birth certificate, a resident alien card, or a Medicare identification card.
If membership in an organization (like AARP, AAA, or a professional organization, for instance) entitles you to a travel discount, be sure to carry that membership card with you when you travel. The one time you forget to bring the card could be the one time you are asked to prove your membership.