A friend at work said she buys everything with gift cards as she can earn cashback. This site shows you who gives you the best rate for them, you get the cashback rightaway so no waiting around. We do our weekly shop at Tesco where were earning 5% back, i'll often just buy the gift card for the exact amount when im at the till!
https://www.mysidegig.co.uk/gift-card-cashback