What chemicals, when mixed, explode or expand violently?!

The most common and powerful explosive you're likely to have around the house is plain old gasoline. It reacts with oxygen, a chemical so common all you have to do is open the windows to get it. Engine designers use gas for a reason: it's cheap and effective.

They also have the advantage of being fluids, which makes it easy to pump into a combustion chamber for reaction. Even better, the result products are a gas, making it easy to pump out so that you can begin the next reaction. (Or, they flow out easily if you're building a continuous-combustion engine such as a Stirling engine or rocket motor.)

No other chemicals you're going to be able to lay your hands on are anywhere near as effective as gasoline. In fact, you may want to work with something with a lower energy density, such as alcohol, vegetable oil, or butane. Or thin your gasoline with water. Work with EXTREMELY small quantities, to keep from hurting yourself. The stuff is astonishingly powerful.

You're unlikely to find anything cheaper or more common. There's no need to go to specialty catalogs to find abundant sources of energy.

Potassium permanganate has been and still is used for many things. Stradivarius used a solution of KMnO4 to stain his violins, and solutions of differing strength are used as disinfectants, etc today.

Glycerol or glycerin(e) is a viscous liquid used in many liquid soaps, etc.

When you mix the two together, the potassium permanganate readily oxidizes the glycerol in an exothermic reaction that produces smoke, heat, and eventually a flame.

The reaction does take some time to start (depending on the amount of water in the samples, grain size, etc), so if you're looking to speed things up you might want to consider ethylene glycol instead of glycerol. Be careful though, ethylene glycol is poisonous.

I think you are looking for Vinegar and Baking Soda.

Anything more than that, I am afraid would be in violation of the Terms of Service of this website, not to mention alert the FBI to your activities.