There are several reasons to keep your receipts for restaurant meals. If your meals qualify as business expenses, for example, your receipts will substantiate either your employer's reimbursements or your income tax deductions. Many people also keep their receipts to compare them to credit card statements. Tracking restaurant receipts is also a good way to plan and budget future expenses.
Keep the customer copy of the credit card receipt together with the itemized bill that usually accompanies it. You will typically get a copy along with the restaurant's copy that needs to be signed. This will occur at sit-down restaurants where you pay at the table.
Remember to take the receipt when your waiter brings it with your change from a cash payment. If you told the waiter to keep the change, though, you should specifically ask for the receipt. Of course, if you pay a cashier prior to leaving the restaurant, you'll be handed a receipt.
Request a receipt when you order at a fast-food restaurant. More times than not you won't get a receipt with your meal, so you will need to get it from the cashier before you move down the line to wait for your food.
Ask for an itemized receipt if you aren't given one with your bill and your employer won't accept a credit card or cash receipt on its own. Some employers like to see exactly what was purchased instead of just a payment slip.