Most people don't know you can tip your flight attendant! It's, of course, not required by any means, but they would gladly accept them. One flight attendant even shared, "If you offer me a gift, or even your used magazines, it's appreciated, and I'll see what I can do to take care of you!" It's the thought that counts and can really go a long way. Maybe they'll even give you some snacks for free.
Most service workers receive tips, so why not share them with those taking care of you on your next flight?