1) Shoes. (Made in China. Can't find them there.)
2) "Wicking" shirts for running and working out. (Ditto.)
3) Dental floss. (No big evidence of its use there.)
4) Books in English. (Easy to find in Japan; harder in China.)
What you would like to be able to take back:
1) Ability to get a reasonable haircut.
2) Wine other than Great Wall, Dynasty, or Changyu. Ie, wine that tastes different from Pepsi.
3) Ability to see real newspapers each day -- experience of scanning the whole page is still different from article-by-article scanning on the internet.