Taking the stairs or parking far away
This shouldn't be your only cardio activity, but the results will definitely add up. Instead of the escalator or elevator, take the stairs. Get in the habit of parking your car at the back of the lot so you have to walk farther. Try taking 15 minutes of your lunch to walk. It all adds up to more burned calories every day.
The body does burn a higher percentage of calories from fat in the 'fat burning zone' or at lower intensities. But, at higher intensities, you burn a greater number of overall calories which is what you should be concerned about when trying to lose weight. The chart below details the fat calories expended by a 130-pound woman during cardio exercise: