Hi Victoria!
Welcome to planDisney.
It's always a pleasure to assist my fellow guests from the UK, and I'm happy to answer this question for you.
You may use several payment options around Walt Disney World. Credit and Debit cards, along with Disney Gift Cards, and cash in US$ are accepted. Your Post Office currency card should be fine as it's a pre-paid Mastercard, and Mastercard is accepted across the whole Resort - at the theme parks and water parks, at the Disney Resort hotels and at Disney Springs. I have never had any trouble using my pre-paid currency cards - FairFX, Revolut and Monzo - when making purchases or linking to my My Disney Experience account.
If you love to shop, you'll love Disney Springs. For the widest range of souvenirs I highly recommend World of Disney (the biggest Disney store in the world!). I also love Trend-D for some unique boutique items of clothing and jewellery, and the Marketplace Co-Op for an assortment of retail venues for a great selection of Disney homewares and candles, and some lovely vintage-style Walt Disney World theme park t-shirts. I recently visited
D-Tech On Demand for a new personalized phone case!
Here is a map of Disney Springs so you can see where everything is located. I highly recommend Ghirardelli Soda Fountain and Chocolate Shop for the best coffee at Walt Disney World (in my opinion) and if you are feeling indulgent you can't miss the World Famous Hot Fudge Sundae or the Vanilla Shake!
Please come back and visit us if you have any further questions, you can also
send me a direct question if you wish. We will be happy to help you plan your magical holiday to Walt Disney World!
Sue