I'm sure a lot of Ryanair's revenue on board is from food and drink. If it costs them 30p for a can of Coke they then sell for say £2, that's a decent profit.
Food, scratch cards, alcohol etc. must add up, but doubt it's anywhere near £24k. There wouldn't be the space for passengers if the aircraft was being used as a warehouse. £24k is probably daily for all their flights.

Only thing I've ever had on board an aircraft was a bottle of Lapponia on a Finnair flight, although I pre-ordered that from their website as it was around £2 cheaper that way than in the duty free shop.
Was tempted by one of those model aircraft on a stand after seeing one in the lounge foyer.

Duty free is generally a rip off, although there might be the odd thing there you can't get elsewhere, or need. Toberlone £4 in Tesco Vs. maybe £7.50 in duty free (although 3 for 2 a lot of the time, so around £5 each if you want 3 - the normal price in supermarkets)
As for the 2x price of sunglasses, remember things like that pre-Covid on BA. Looked at a worldwide travel adaptor, Skross or something, and that was a good £10-£15 more than I paid from Amazon.