We took E shopping tonight to get Grandpa a birthday gift. She loves shopping, and insisted on bringing her purse and wallet. Her wallet is filled with "money" which is really coupon cards from various stores. At our last stop of the night, she walked around the store picking up items and saying "three dollars" and then putting them back on the shelf. According to E, every item in the store cost three dollars. Then, on our way out, she grabbed her "money" and said to the cashier "pay money."
I'm not really sure why E understands commerce so well, although she grocery shops with dada over the summer, she doesn't really shop with us that often. I guess she's ready for an allowance.