I often take little gifties. A sealed pack of Ferrero Rocher in the sturdy clear plastic box, with enough for each of the crew. I print up a little note saying how I appreciate their basically walking a marathon on their aching feet while I sit back and watch TV.
It's just a little extra – a few bucks in Coles when they are on special which they frequently are – and it makes people smile. I like making people smile.
I don't expect anything back. Sometimes it sinks without trace, sometimes I get an assortment of extras – a cap, a postcard, a pen – but that genuine, open smile is reward enough and it lifts me up, because sometimes I've had a stressful day too.
I did once use this as a kind of bribe and it worked superbly well. The story is
here.
Thoroughly endorse using the feedback system to supply praise for any crew members who did an excellent job. Some of these FAs go above and beyond. Worth checking at the end of the flight exactly how their name is spelled and why you want to know.