STYLETHREAD -- LET'S TALK SHOP!

As background: I'm in a mentor program where I have been paired with various preceptors over the past year and worked with about half of the people in my department (whole department consists of about 20-25 people).  Part of the program required me to move to another department after 1 year.  Since I will be moving to a different department and a different floor in the building, I wanted to thank everyone I have worked with over the year.  The caveat is that there are about 4 people who have spent significant time mentoring me, sometimes hours a day.  There are several other people in the department who I have worked alot with, just didn't receive as much mentoring, and then there are yet other people in dept where I have not really interacted with them at all.  The problem is, I don't want people to feel left out and having trouble figuring out where to draw the line. And I was thinking of just getting a big cake for everyone, but we share our floor with other departments so it would be difficult to find a place to put it without being eaten by others. To further complicate the situation, I may have the opportunity to get hired on and work with this department in the future after my mentor program is over.  Any advice or experience would be helpful! I am currently thinking of going with a cupcake and cookies in a bag, and putting it on everyones desk?  But would like other ideas and the politically correct way to handle this!