Inherent in tracking everything about our bodies is tracking the environment. Anything that enters our eyes and ears could be relevant; that could mean any sort of nice, organized environment that makes us feel good and think in a positive, organized way.
Everything that we breath is relevant thus the details of the materials around us - and what's in the air.
All things are on the table for tracking. Some things will be less significant adders to our overall life experience, sure, but until we've collected the data for decades and graphed the correlations, we won't know the exact answers.
Now, it's also possible to collect data that already exists - by accurately questioning people or tracking our own past as well as possible. This data isn't as pure as collecting accurate data live, of course, but it's still there for the collecting.
We really just need global leadership that motivates everyone to this task and we would learn amazing things very rapidly. The harder we at QS push, the sooner this global effort will really get going and the world will change in an amazing way.