I never got an RFE, but for those of you who do, I think this will help you in case you have no other proof to send in. I sent in Paypal receipts for online purchases to cover from 2009-2012. I also sent them some facebook check-ins and a few photographs with the dates and location on them.

That was my evidence to cover continuous residence for 3 years and I got approved today. So if you get an RFE, you can use that stuff as evidence.