Storing your BTC on an exchange is the common way most traders save their coins. But is it the best method? Cold storage to me look expensive, since it is costive to purchase hardware.
Cold storage doesn't always require purchasing hardware. If you make a "paper wallet" you can do it for fairly cheap, you could then laminate it and stick it in a safety deposit box. You could also make a more "substantial" wallet if you have access to an air-gapped laser cutter. You could engrave it into a metal sheet and then place it in a folder to prevent other people from seeing it and then place that whole packet into a safety deposit box. This method would also allow for a bit more durability and general survivability. The odds of a bank robbery are incredibly low, but you could also disguise your key in a method of your choosing before recording it. For example, a typed page that looks innocuous unless you know how many words to count over on could hide your key from even someone who is staring at the page AND knows that your key is hidden in the writing.