Lots of shops give you a paper bag for your goods at Christmas and in the sales, especially clothes shops. These bags often have string, cloth or ribbon handles. There will be two, identical pieces of material if you pull them off the bag. Do so and save them.
Every now and again you will need to break a large group of people into pairs and you will want them to work with a relative stranger rather than a best friend.
Have a container full of pairs of former bag-handles. Shuffle them and shake them. Ask everyone to draw one out, blind. Then ask everyone to find their partner; the person with the matching handle.