No. If you don't make the purchases you won't get paid.
And you can get as much gasoline as you want, you will be reimbursed for $2. Same goes with your purchase in the store, you can buy anything you want, but you'll only be reimbursed $1.
I buy ONE gallon, no matter the price. And I buy the least expensive pack of Planters peanuts I can find. I buy Planters because they are usually the least expensive item that isn't penny candy in the store and they are usually under $1.