Whether you do a same-day turn or just an overnight, definitely leave all your luggage in Shanghai (at your hotel or at Left Luggage at the airport) and take just a minimum as a carryon--briefcase or daypack. If anybody at the destination airport gets confused and asks, the truth (that this is needed to fit China's TWOV requirements) isn't a bad option. Or if the turnaround is several hours, the excuse of "a friend wanted me to pick up some genuine kimchi" (or whatever the appropriate cultural souvenir item may be for that location) is usable.