I took some cards from Me & My Big Ideas that I got at Michael's and made them into favors. All you have to do is tuck them into plastic glasses and fill with candies. You can do this for a party or for a holiday dinner. If you want, use a permanent marker to write the guest's name on the glass.
The next idea I have for you is to create a calendar for your desk or as a gift. Take an acrylic frame from the craft store (about $2) and use cards as the background. You can insert holiday-themed cards, baby-related cards or wedding-style cards if you're giving one as a gift. If you google the words mini calendar, you'll find printables to make your own calendar. Easy and fun to make!
What do you do with your extra cards? I have a bunch to use up :)