Challenge Me!!

I enjoyed challenging myself to the Seven Days Without Coffee and documenting the process very much.  So much, that I'm already thinking ahead to the next challenge!  I have a few ideas of my own; such as 7 Days Without Sugar, 30 Days of Exercise, or 7 Days Without Gluten.  But I could use your help! 

What should I challenge myself to next?

Please leave your reasonable challenge ideas in the comments.