Many people here suggesting a throwaway email and/or VPN. While this does migitate the impact somewhat, the only proper response is to not use their "service" and deactivate the WiFi fo your phone (else they might be tracking your MAC address).
Walmart has an interesting app where if you're connected to their wifi then the app "transforms" to tell you what's in stock in the store you're connected to. I wish they'd just do something like Home Depot where the site just tells you if X location has an item or not, but alas.