For smaller stuff you could use glass jars for salsa, jelly, etc. any tin containers you might have. For bigger stuff you could use pallets that haven’t been treated with methyl-bromide to build raised beds or use it as a plant stand. Or if you want to go the rural white trash route you could use old tires that you paint usually some pastel color.

Old plastic bottles cut in half, milk cartons, cups especially the polo ones, old Tupperware, egg cartons for seed starting, etc. I’ve also seen some cheap pots at dollar stores, pretty good sizes too, though I never tried them out before. Just remember to drill some drainage holes.

I use yogurt containers

I’ve seen a neighbor use milk crates lined with old t shirts, but if you’re putting the planter directly on the dirt you only need to line the sides with newspaper.

A lot of people use landscape fabric to line them, which is overkill and prevents the bottom of the soil from coming into contact with the ground. You want the worms and good bacteria to go up into the planters.