If you just bought a manual miter box, a simple modification will extend its useful service life. Insert and fasten a piece of 1x stock to the inside bottom of the box. The saw blade will then cut into the false bottom, without damaging the miter box itself. Occasionally move the wood back and forth, or turn it over, to spread out the wear. When badly cut up, just replace the piece.
Run your air conditioner for a few minutes in the spring, before you need it. If you wait until the first hot day to discover is isn’t working, you’ll find yourself on a waiting list, sweltering sometimes for days before an air conditioning specialist can come to fix it.