Wow! If you shop at Tesco you need this in your life. Get a free month trial of Clubcard Plus and that will give you 10% off any 2 of your in-store shops. You can pick whichever shops you like so save it for your big ones and you can save up to £40 a month.
If you want to continue it's only £7.99 a month so it's well worth continuing if you're a Tesco shopper. If you're doing 2 shops a month which are more than £40 each then you're crazy not to take advantage. Plus you get additional benefits too including 10% off Tesco brands. Best of all you can cancel at any time.