Barclay just creates a holo program where he returns the cart along with all of his friends and they thank him for it. He has never been to that store.
They are themselves abstraction layers for the apps that are made for them. Software has many levels of abstraction from what you see on the screen all the way down to hardware.
For #3 and for people that might not have sodium citrate handy, adding a slice of American cheese to cheese sauces will do the same thing as there’s plenty of sodium citrate in there to go around.