I was going to say you are obviously being unreasonable but actually costing it out when you are trying to buy for a single person, which I imagine you may be when catering for someone who's visiting and not part of the family. This is just a quick example I've put together based on stuff I typically buy, and when trying to provide for one person it is still weirdly expensive. However it's still well in budget and is quite a nice varied shop.
Breakfast - 3 days = oats so simple porridge and a banana. 3 days = Scrambled eggs on toast/ hard boiled eggs and toast. 1 day = blueberry pancakes. Accompanied by glass of fruit juice and tea/coffee.
Lunch each day - various sandwiches, veg crudites with either hummus of Philadelphia, fruit pot, savoury snack, crisps.
Dinners - Mushroom and cheese omelette, spaghetti bolognese, nicer ready/oven meal, beans on toast, stir fry, soup and crusty rolls, takeaway.
Small punnet of blueberries £2
Bunch of bananas - 75p
6 medium eggs - 89p
Butter - £1.50
Pancake mix - £1
4 pints milk x 3 for tea, coffee, cereal etc - £3
2 x bottles of fresh juice for 1 glass with breakfast - £2.70
Oats So Simple Big Bowl - £2.20
PG Tea Bags x 40 - £1.40
Small jar of coffee - £2
Small bag of caster sugar for tea and coffee - 60p
7 x little lunch side e.g. fridge raiders, olive pot - £8
7 x various fruit pots - Tesco do a variety all for £1.15 each = £8.05
Loaf of nice bread - £1.50
Block of cheese - £2
Pack of naice ham - £3
Romaine Lettuce - £1
Tomatoes - £1
Peppers - £1
Carrots - 50p
Hummus - £1
Garlic and herb Philadelphia small - £1
Large cucumber - 60p
Bacon - £1.55
Branston Pickle - £1.55
Helman's Mayo - £2
Multipack Walker's Crisps - £2.50
Jamie Oliver tray bake meal - £8
Spaghetti - 55p
Nicest pasta sauce - £2
Pack of bolognese seasoning - £1
Mince beef 250g - £1.80
Heinz Beans - £1
Mushrooms - £1
Hard cheese - £2
Takeaway - £20
Fancy soup carton - £2
Crusty rolls - £1
Stir fry deal with fresh noodles, veg pack, sauce and protein - £5
~ £100
FYI the lunch stuff works out actually cheaper to buy a meal deal but there's more food and you'd have leftovers plus some of the veg is used in the meals.
But yeah that clocks in at around £100 and it's way on the higher end of what you'd need to buy. You could provide someone a decent menu for half that or as a PP said, even every meal out would be less than £21 per day.