I always buy chocolate for the crew because I love when other staff passengers do it to me.
Same here flybywire 
We know how stressful it can be to fly on std by tickets, and it is nice to look after each other. I always try to get an upgrade for collegues, even other airlines'.
BTW, Just flew there and back EDI (4 sectors, via LHR), and boy, BA CC (and check in staff I must say) are GOOD! Friendly, efficient -well- professional!
I was really impressed in particular by how they carried out a full service with hot meal on a 1 hour flight, finding the time to do a second passage of hot drinks in a full A320 
And all that with perfect courtesy and a smile.