Regarding clothing: I've heard the idea that we'll all scan our bodies, upload that data, and an online site will be able to show us what will fit us.

People may find that too creepy, but Amazon could do something else: gather lots of feedback about what fits customers and what doesn't. You get 3 pairs of pants, rate them "too big" and "too small" and "just right". Eventually that could correlate that if you and Customer X both fit these pants recently, the shorts he bought last week will probably fit you too.

(This would be more complicated for women, of course.)