To copy foods or a whole meal from one day to another, use the ⋮ button to the right of the food or meal header.
Then, select Copy To... from the menu. A calendar appears.
Choose the date and select Set.
Next, select the meal where the food will be placed (copied to). Once selected, you'll see a message saying "Items copied!" across the bottom of the screen.
Navigate to the date you specified and you'll see the food or meal copied/logged there.