If you have a contactless card . You may want to try this before hand to make sure it works with your card. Also to make sure the times etc are in level with your budget. If you get this wrong then you will end up paying charges etc.
If you have a contactless card then depending on how long you need the money for. In theory you can have multiples of £30 available in your account and you can spend this several times over.
The way this works is. Some companies without naming them. I mean major shops when paying by contactless will take upto 6 days to take the money from your account. Also as a fact these same companies will not hold these payments untill processed.
If you pay by chip and pin. This will automatically put a hold on however much you have paid. Although the money is sitting in your account. You cannot use it. However with contactless some shops will immediately hold the payment. Where as others will not. They will not even hold a quid. The payments then come of after a certain amount of days. I have seen this being tried. It works but you need to like i say know what sort of times are involved. The same as paying for petrol/diesel via a automated pump.
For example :
Tesco will take 3 Days to debit your account with the amount. However £1 will be held .
Sainsburys does the same but can take 3-4 days and also over bank holidays this extends their time further.
Morrisons will take a £1. and take 4 days to debit and even five depending on if you filled up during the early morning or late evening.
Shell will debit the follwoing morning . Sometimes 2-3 days later but will hold £1.00
Bp + Esso the following day depending on where it is.
People are going to slate me. If i am even helping one person it is worth it.
The coop contactless payment never shows. they take 5-7 days in collecting it.
Sainsburys again 3-4 days before collection.
Tescos 2 days
Poundland etc 3-5 days.