We get the word out to all the teachers in our school when a student teacher is leaving and the school secretary keeps a box by her desk for donations. Teachers either buy something for the student teacher's future classroom or hand in something that they have duplicates of, no longer use or need, etc. Generally, these boxes are overflowing with different gifts and student teachers are always grateful.
Also, I have, with the help of a room mother, videotaped each child in my classroom saying something they'll miss or really liked about my student teacher .. and included it in a DVD that we put together.
The books by Mailbox with hints on what to do on the first day of school, or such books that contain general information about classroom management are also appreciated by someone who is just starting out.
Hope this helps!