Decide what you're making.

Go shopping. You have a limited budget of just £50.00.

Buy your ingredients from the local (online) supermarket. You're going to prepare a 3-course meal: starter, main course, dessert.
And don't forget appropriate drinks.

Write down the recipe of your 3-course meal. (ingredients + preparations)

Who knows, if you still have money left over, perhaps you can buy him/her a small present.

Just to be sure, you need to keep the receipt. So write down all that you've spent.
IMPORTANT: in Britain the currency is the Pound Sterling (£). Be careful with prices... €10.00 is not the same as £10.00 (although there isn't much difference these days)