There are so many simple things you can do to burn more calories in one day, especially if you live and work in a city.
Instead of taking the subway, bus or cab to work. Walk. I am not saying do it everyday (especially if you're running really late), but try briskly walking to or from work at least once this week. If you like it, next week try doing it at least twice. Slowly build up to doing it all of the time.
Live too far to possibly walk and still make it on time? Well then you can still take the subway, but get off a few stops earlier and walk the rest of the way. You could burn upwards of 69* calories for every 15 minutes of briskly walking. You'll burn more if you're carrying a load, like your laptop and purse.
*Based on a 140 pound woman.