This isn't as hard as you think. Place an optical indicator (like a QR code), on a piece of paper, and put it where you want the groceries to wind up. Drone finds your house. Finds your landing spot (which was presented to you via a nice "print this" dialog when you ordered), and sets the stuff down.
Alternatively, if you're going to be doing this, you can purchase and register an IR beacon that is more permanent than a piece of paper.
It's not that simple. There are a lot of people living in apartments - how's it going to work for them?
And where exactly would you place the indicator? In your front yard? Normally, delivieries are made to your porch, but the drone would have difficulty finding an optical indicator on the porch from above.
And what about groceries that need to be refrigerated? Those will need to be dealt with specially.
Oh noes, now I only have a business that delivers groceries to people with lawns. What a tiny niche business:) Seriously though, those are really lame problems. If I could sign up for a service that uses a geofence to find out when I get home and then f-ing airlifts milk to the dead center of my front lawn, I would buy so much milk.
Alternatively, if you're going to be doing this, you can purchase and register an IR beacon that is more permanent than a piece of paper.