Save yourself some money and stop adding to landfill by getting in the habit of taking a reusable shopping bag out with you. Always. With so many lovely designs, and bags that fold up into their own tiny pouch - there really isn't any excuse for buying yet another 5p single-use plastic bag at the checkouts.
Make sure that your reusable bag is machine-washable. If you have a clean bag with you, then you'll be able to use it for buying loose produce when you see it e.g. packaging-free bread in Lidl or from a local bakery.
Don't be fooled by paper bags - they are single-use too and most paper requires trees to be felled and lots of precious water to be used up.
So, get into the good habit of carrying a (washed!) washable reusable bag with you.