One of the blessings of being transient is the sheer number of friends that you build up over time. One of the downsides of that is that you can lose touch with them. The ones who are really on top of it, keep their address books current and send you annual Christmas cards.
My parents had a post-holiday custom that my family is trying to implement. I think it's really easy and practical.
Instead of stashing those Christmas cards somewhere or throwing them away w/ a twinge of guilt, try something more "guilt-free": Every night at dinner (or any meal), take one card a night and pray for that family even if you may not know them really well. Pray for marriages, children to come to faith in Jesus, deeper Kingdom commitment and whatever else. Then throw the card away.