It is annoying when you buy food packed in plastic bags, only consume part of it and the rest remains in the bag, which you cannot close properly. Biscuits can become soft and buns hard and inedible.

To seal a plastic bag well, all you need is an empty plastic bottle with a screw cap. Cut off the neck of the bottle and unscrew the cap. Now push the plastic bag through the bottle neck from below and fold it over the bottle cap. Then screw the lid back onto the bottle neck with the plastic bag in between. Now the plastic bag is waterproof and airtight.