What are /r/retardsinaction's favorite Products & Services?

From 3.5 billion Reddit comments

It’s for this book: The Back of the Napkin (Expanded Edition): Solving Problems and Selling Ideas with Pictures https://www.amazon.com/dp/1591842697/ref=cm_sw_r_cp_api_glt_fabc_RN13SYZ2AH4HTEH2RHF5?_encoding=UTF8&psc=1