Quadrum Origami Box
Kate (Quadrum Game Designer) made over 100 of these boxes, made out of old sheet music, to hold her chocolate wedding favours. It's a nifty little box that is all around the internet, so if you don't like my instructions below, you can always use the instructables one or watch a video. You are not at all obliged to make the box if you don't want to - you can store your cards however you wish (e.g. snap-lock bag, envelope, simple rubber band, etc.).
Step 1: Print and cut out the template
Step 2: Turn the paper so the printed side is facing down
Step 3: Take each of the corners and fold them into the middle of the square (i.e. fold along the line)
Step 4: Fold the top and bottom sides to meet in the middle, then unfold again
Step 5: Do the same thing to the other two sides, then unfold again
Step 6: Unfold the left and right sides
Step 7: Fold the top and bottom sides to meet in the middle