Farewell gifts try to give a continuing shape to a changing connection.

A present at a leaving is an attempt to continue something that is about to become uncertain. Nobody yet knows what the friendship will be once the daily contact stops, so an object stands in for the answer. It is a hopeful act rather than a confident one. The gift says the relationship should persist without being able to say in what form, which is exactly the position both people are in.

If someone is going, say what you hope will continue rather than leaving the object to say it. One clear sentence about how you would like to stay in touch does more than anything you could wrap.