I was a cast member in 2003 and, assuming the rules haven't changed, cast members are not allowed to accept gifts or tips. The policy is for the cast member to politely refuse 3 times and if the guest insists then they take it and donate it. I had that happen one time, a guest wanted to tip me for helping him find a jasmine costume for his daughter and even after refusing 3 times he insisted so I took it and gave it my manager.
If you wanted to give a gift to a cast member, find one that has gone TRULY above and beyond and then stop by guest relations and fill out a comment card (they have a fancier name, I cant remember off the top of my head). Those actually speak volumes and are very well respected.