My sister and I always do my parents stockings, since we are older now. I like to put little scrapbook accessories and things I can find cheap or on clearance at local craft/scrapbook stores.
We always get them both new desktop calendars, my mom gets a dog one and my dad gets one with funny quotes or something.
We like to put little 'everyday' things in there: tic-tacs, batteries, car air fresheners, favorite snacks (my dad loves nutty bars.)
Anything *insert local sports team or college alma mater* related.