-Bill is the paper which you have to pay. -Receipt is the paper which you recive after the pay.

The bill is like an "invoice". The receipt is confirmation/proof of payment of the bill.

It depends entirely on the time when the statement, "That was an expensive meal." was made. If after the meal, but before paying, when the bill is available, it means the bill. After paying, the bill "goes away" and you have a receipt, so you'd use receipt.