I'm not a teacher but I work in a secondary school as part of the pastoral team and often receive gifts for Christmas or from Year 11's/13's when they leave. Most of the students I work with have had a difficult start in life and are hypersensitive to rejection (or perceived rejection) by adults. If I were to refuse to accept a gift, as pp have suggested, these children would without a doubt experience this as a rejection of them personally. The gifts tend to be things like flowers, smellies or chocolates, wine, once it was a book, so nothing too extravagant. Of course I don't expect it or feel I am owed in any way, but I certainly appreciate it.
One of my most treasured possessions is a charcoal drawing a student did of me- she made me look much younger and more beautiful than I actually am, bless her! I also love getting cards from students or anything homemade really as it's touching that they've gone to the trouble, although again I don't expect it.
Anything edible (biscuits, chocs etc) tends to get redistributed to students anyway as I have a drawer in my office full of snacks, San pro, tights, stationary etc etc for students who, sadly, come into school underfed or ill-equipped.