Beef people form a group, pizza people form a group, etc. Like colors work together. Like colors work together. Like fields work together. Write a number on a piece of paper without letting anyone else see.
Close numbers work together.
When students enter the room, I offer a basket of different kinds of candy. Students selecting the same kind form a group. Like numbers work together. Students wearing red work together, blues work together. One day stripes work together, plaids work together, boots work together, tennies work together.