I always want to snack at work. Vending, snack shack, whatever. But I've found that if I sit for even 3 minutes and just write whatever comes to mind, never stopping, I get over the "hunger" for snacking faster.
Free writing is just that. Write about anything. Describe what you see in front of you, record your thoughts about the day, anything. The key is to not stop writing for 3-10 solid minutes. Then go back and read what you wrote, you might be surprised!