On way back I stopped for gas. It was a rural Pennsylvania gas station on US-30. The only purchase I did the whole day was a pint of chocolate milk from the gas station. A brand I had not heard before, local to Pennsylvania. I paid cash $1.13.
Today I am seeing a "suggested post" on Facebook - organic milk of the same brand!
I don't use Facebook on phone. My phone has no data plan.
But Facebook found out I bought chocolate milk!
They know a purchase of chocolate milk from the gas station as the cashier had to scan the item. From the cellphone tower records (a T-Mobile prepaid connection) they narrowed down the choice. I was in the area when the purchase was made.
T-Mobile would have saved the pre-paid account activation IP, which Facebook knows too which I use to browse. They know the SIM was at the gas station.
The moral of the story...they are going to track and infiltrate whether you use cash or coins!