Before you begin make as many groups or pairs as you will need for your activity. Then have each student pick a card and tell them they cannot let anyone see it. After all the cards are distributed, explain that they have to find their other group members by using only hand motions or body motions. They can't use words or show their cards to anyone. It's a blast to watch.
Students give birthdays.
I write these on the board and then put closest birthdays together. I also do this with last four digits of phone number, house number, parents anniversary. Beef people form a group, pizza people form a group, etc. Like colors work together. Like colors work together.