Surveys
Three or four times in my adult life I signed up to fill out surveys for a couple different testing institutes. I was part of the team that tested things sent to me. When those products were officially released a couple years later, I recognized them. I was told never to tell anyone that I had been part of testing them, probably to prevent competitors from finding out.
At one point I was asked to fill out a two-week food diary for the eight people in our home. It was crazy complex; everything we as a family ate, who ate it, how much of it they ate, brand names and type of store we got it from. I got paid I think five dollars and a pair of headphones. I enjoyed filling out the form. I learned what we were actually eating, but wouldn’t want to do it again. My husband thought I was crazy for putting in the time and effort. I enjoyed the nit-picky-ness of it. It was fascinating to figure out… once.