well, then i would say not having any other facebook apps and important information that could be stolen by the instagram in the phone, or use it in web-browser in some privacy mode or separate container, something like that. use disposable email.
using wifi in mcdonald is silly advice, i guess you are not being hunted by some secret service, there is really not much somone can do with your ip address, which is most likely dynamic and nated anyway. if you had some fixed ip address that would identify you, that might be another story.