How would this differ from keeping your hotel keycard, ID card, cash, and credit cards in your wallet/purse? If you lose your wallet/purse in that case, you'd also have no key, no ID, no money, etc.
Perhaps Apple Wallet will act as a secondary but a fast path access and I'll continue to carry physical IDs but don't have to pull them out for most of the cases. That is how I used Apple Pay. I carried bank card with me but used Apple Pay 99% of the times.
That said, I don't really like a single electronic device being such a single point of failure. (And, to be honest I find taking out a card easier than Apple Pay most of the time.)
Yes, that would be more expensive if you don't already have multiple devices. I'd wager than many people here on HN (who are in the Apple ecosystem) have at least 2 devices on which they could add payment/IDs/access (Apple Watch, iPhone, iPad, MacBook).
On the note of charge, Apple has recently included a feature that lets certain cards work even when the phone doesn't have enough charge to be normally used. It seems they shutdown the phone before the battery is entirely depleted, reserving a small amount of charge to be used for these cards.
https://support.apple.com/guide/security/express-cards-with-...