It's not really to the detriment of the customer though.
If the shop keeper has 2 shirts left and decides to charge a pound. If the Offer was made by the shopkeeper and the Acceptance by the customer, then the shopkeeper cannot decline the contract once the customers says, "I would like that...
The issue at the club is that the tills don't appear to be clever enough to know that pressing the buttons for "Hot Dog" and "Pint" is the same order as pressing the button for "Hot Dog & Pint Meal Deal".
The simple solution is...
Customer: "I would like an £8 meal deal please"
Student behind...
The invitation to form a contract is made when you (the customer) make your offer of payment.
The acceptance is made when the shopkeeper takes your money and agrees to the sale.
Everything else, including advertised price etc, is just customer service issues and has no importance in legal...