What are some cheap, easily available products or lifehacks that replace normally expensive items or habits?

Recently, while looking for a way to clean a burned pot, I came across a method that required just some vinegar and baking soda — and it worked wonders for me, as well as being practically free. Inspired by this experience, I started searching for more uses of common products (soda in particular can be used in a multiple useful ways).

Do you have any tips and methods that allow you to avoid buying ridiculously overpriced cleaning (et al.) items and reduce the plastic waste? Feel free to share :)