What should you measure?

One of my thrusts this year is to understand myself better using data and objective analysis. 

The way I am going about this is to collect whatever data I can, look for patterns, form hypotheses, and then try to verify them.

Online activity, Phone calls, location are some relatively easy ones. RescueTime can help you track your computer activity, phone logs can be obtained (with difficulty) from phone companies, and location data from foursquare or a similar API. Fitbit tells you how active you were. These require little effort,  but might not give all the information you need to measure performance.

Other things like mood, productivity, output, food consumption are more specific but require more effort to collect.

The challenge is to figure out how to collect maximum relevant data with minimal disruption.