Gifts are not required, but they're always appreciated. I would get one for someone I really cared about but not for a random cousin, unless they or their family had given me a gift in a similar situation.
Gifts can be something they can use for their professional field (i.e. a briefcase, organizer (digital or paper), etc.), jewelry (a watch for men, or a simple pendant for ladies), or a nice gift to treat themself after their hard work (like a Starbucks card, spa gift certificate, or restaurant gift card).
You don't have to spend a lot--a $10 card to Starbucks and a warm note saying how proud you are of their accompishment really means a lot.