O'Sullivan & Hilliard's The Law of Contract (2018 8 ed). p. 90.
5.5 Better still, keep in mind some common examples of consideration in practice:
• Simultaneous contract and performance, like sale of goods at a supermarket: you get the goods and provide, by way of consideration, the price in return; the supermarket gets the price and provides, by way of consideration, the goods in return. Contrast this with a gift of goods—the person making the gitf gets nothing in return and therefore the gift ‘transaction’ has no consideration and is not regarded as a binding contract. Of course, the relevance of the distinction between a binding contract and a purely gratuitous exchange is more significant where there is a gap in time between the formation of the contract and the date it is to be performed, as in the next category.
• Bilateral contract made before it is due to be performed, as where A and B make a contract in January for the purchase/supply of grain in August: A’s promise to pay the price is made in exchange for B’s promise to supply the grain—the law regards A’s promise as the consideration for B’s and vice versa. So there is a binding contract in January even though nothing is to be physically handed over until August. (Notice there is no external logic to this principle—A’s promise is only good consideration for B’s because the law regards it as enforceable and therefore of value, and it is only regarded as enforceable because it is supported by consideration. But it is only supported by consideration if B’s promise is enforceable and so it goes on ad infinitum! Despite this, it is a hugely important commercial principle.)
What does "it" refer to here?
What 'consideration' is being referred by consideration?