The best thing I bought was a heavy cast iron camp stove pan (really a grill for over a fire, it has 1/4" edges). It was less than half the price as a cast iron pizza "stone" at a famous cooking store. They have round and square. They do not absorb odors like ceramic stones and can take blazing hot temps and hold them steady.
That was the best cooking tip I've ever received (from a pizza fanatic) and I pay it forward. Enjoy!