Seeking Authentic Bangkok Experience

Hello everyone :)
I'm visting Bangkok Dec3and7, it will be my first time.
What would you recommend as the top activities, restos, and things to do?
I'm interested in knowing:
is there traditional thai medicine or beauty treatments i should try?
What thai brands should i shop for?
Which cabaret do you suggest i see?
any cafe, food street, or resto i should visit?

All help will be greatly appreciated and favours returned should you visit Shanghai.

Best Regards,

Melissa