If you just need to stretch your legs and get out of the office for a bit, offer to do a coffee run or drop off mail for your co-workers. This way, your extended break actually crowns you the office hero. Helpful hint: if you offer up a late coffee run around 4:30pm, youre less likely to have to juggle 8 cups of Starbucks on your way back.
Learn the magic of alt-tab (or apple-tab on a Mac). This keyboard shortcut scrolls through your open windows quickly, ideal for when your boss's heels are clacking down the hallway. It's a much smoother response than reaching for the mouse to minimize a window, which can look suspicious to nosy bystanders.