Like how Dave Gorman tried to meet 52 people called Dave Gorman, and this person is trying not to buy anything for a year then will DEFINITELY write a worthy book about her struggles:

http://www.theguardian.com/money/blog/2015/nov/26/black-friday-buy-nothing-day

I reckon a good one would be "A Year Without Fiction" - go a whole year with watching any TV, film, reading a book etc that was a work of fiction. Combine that with some cultural bullshit about the power of storytelling in all of our lives. Bestseller, right there.