While this sounds a good idea, the problem which might be encountered is if you forgot and you got to paying and became embarrassed when the card is rejected. A lot of people get embarrassed over cards being rejected.
So I get this idea is coming from the perspective of controlling your finances.
I immediately think about situations where this would unintentionally backfire. Travelling late at night, need food and sustenance, only option is Pret… travelling early in the morning, only option is Pret… colleague decides to have a meeting in Pret … etc etc. There’s just too many situations where this type of function would be more trouble than it’s worth. Cue messages to CS from people saying: hey I blocked Tesco/Pret/McDonalds but I now need to make a purchase in the next 30 seconds as it’s the only option available to me.
I used to drop off their food to a hostel so I have tried almost everything they offer.
Their sandwich combinations are weird. The only one I like is the tuna and cucumber baguette. Their cakes are nice but way overpriced for what they are.
I however think it’s great that they give something back by giving their unsold food to charities and hostels.