Ah! To clarify, I don't let my investments sit on exchanges. I keep them in wallets off of the exchanges. Thanks for the concern though! If I was leaving my investments on exchanges, that would definitely be concerning. Even the most secure and reputable exchanges are targets and can be vulnerable to hacks. Some people never think that it will ever happen to them until it actually does.
I am looking forward to getting a ledger though. Once I get one, I might invest in and place it in a nifty little fire safe. Might be a little overkill.. but actually maybe not? What if that 21 word passphrase were to get burned up too in the case of a fire? haha :)
I've seen various tips on how to keep your nano s ledger safe, as well as the 24 word key phrase... Fire proof safe is an excellent idea! Also, consider storing the 24 word phrase in an encrypted file on a USB memory stick, then storing this in a different location (parents house for example). One other tip I came up with is to use a book to store your 24 key word phrase in, if you have a lot of books on your bookshelf this can be a nice place to hide it... (please note these are just my ideas and I'm not suggesting that this is what you must do, simply what I have thought about / read about over time).