An interesting calculation is the average power output of a human being. This can be determined from the amount of energy we consume in a day in the way of food. Most of us take in something like 2500 "calories" in a day, although what we call calories is really a kilocalorie. Use this as our energy output per day.

Take the 2.5 x 10⁶ cal and convert to joules, using the conversion factor:

1 cal = 4.186 J

This gives roughly 1 x 10⁷ J. Figuring out our average power output, we simply divide the energy by the number of seconds in a day, 86400, which gives a bit more than 100 W.