Darren McGrady was the personal chef to the Queen of England for 11 years. He's still friendly with his replacement so he knows that her routine hasn't changed since he left and when he arrived the Queen told him that she had eaten the same sandwich since she was 5 years old. He explained it in a YouTube video.
"The queen was served jam pennies in the nursery as a little girl. She’s had them for afternoon tea ever since. The sandwiches are made from bread with a little butter and a spread of jam, then cut out into circles the size of an old British penny. She likes the strawberry jam. The queen would eat strawberries three or four nights a week in if they were in season. Then back to grapes and sometimes blueberries".