large Foam core boards to brainstorm ideas. Ikea Benjamin stools hacked to keep the boards upright. They can still be used as stools when needed and are also great for creating temporary walls for project spaces.
Fill a plastic water bottle so it's about a quarter full, lay it on its side and put it in the freezer. This way when it's frozen you can fill the rest of the bottle with water and have an ice cold drink on the go.