Categories is a simple, speedy warm-up exercise designed to get improvisors thinking quickly and developing simple patterns.
Players stand in a circle, often making "drumroll" noises by slapping their hands on their thighs. The first player will shout a category, for example, "Breakfast Cereal," and each player in turn will name an item in that category - Cheerios, Oatmeal, etc. When it gets to the original namer of the category, they shout out an item in the category, and the next person names a new category until everyone in the circle has had a turn picking a category.
It is most important to keep the circle moving and not stall. While it is preferable to keep thinking in the category pattern, it is okay to shout out a "wrong" answer (ie, Bananas to the above category), and keep the rhythm going around the circle.
This is a fun moderate-energy warmup.