When a was teaching full time I always liked "happy notes" that would go in my "smile file."  Those are the letters from parents and administrators complimenting my teaching. When you are having a bad day or a bad week it is wonderful to look back at those for a pick me up to remember why the heck you're in teaching in the first place.
 
Hand made cards from the kids are always wonderful as are needed supplies such as dry erase markers, glue sticks, paint brushes, and of course books of all types.  Pair that with some flowers from your garden and you are set.  Most established teachers have enough knickknacks and bath salts to last a lifetime. If a child really wants to buy something instead of making a craft take him/her to the dollar store.  I still have Christmas ornaments kids made me from 20 years ago. I write their name and the year on the back of them.
 
From the PTA I always like the lunch buffet in the teacher's room, as well as the assortment of healthy and unhealthy snacks that appear in the mornings of that week.  
 
Number one rule:  Do not require a child to give money for a class gift in order to sign a card for the teacher.  Yes, I had a room mother in my daughter's class do that. even after the principal was notified of this and the volunteer coordinator talked to the mom. The children with no money to give towards the teacher's gift were sad they could not sign the card. Of course I went around her with a gigantic homemade card that I had all the children sign.