in packages, we just tell about ourselves--I talk about whatever hobby I am working on or tell something about my family.  My daughter tells a bit about her interests and activities, and the book she is reading.  Doesn't have to be anything special.  As Ninepatch has said (she is where ALL my ideas come from) just write like you were writing a friend.  We stay away from politics (but do mention that we heard about it from Daily Kos, in case they want to check it out), but wish them the best and thank them for their service.

You might even get a letter back, although they are pretty busy.