How can I use household items/foods to whiten my teeth?

You cannot use any whitening products while you have braces.

Whatever you would try (toothpaste, gel, mouthwash, baking soda, whatever) might make the exposed areas of your teeth whiter, but it wouldn't be able to get under your braces.
At the end of treatment when your braces are removed, your teeth would be two different shades.
You'll need to wait until your braces are removed to consider whitening.

You can't really and don't want to whiten your teeth whilst yourpve got braces. When your braces get taken off, that part of the tooth won't be whitened.
Most whitening kits these days, are whitening trays. It's best to wait until your braces are taken off.

Coffee grounds.