A spare pair of glasses cannot help you find it unless you know where you left it.

A backup only helps if you can find it, and the situation where you need it is precisely the situation where finding things is hard. Redundancy fails when it is stored in the same way as the thing it was meant to replace. The spare has to be findable by the impaired version of you.

So put your spares in fixed, boringly obvious places and tell someone else where they are. This applies to keys, documents, passwords, and to the plans you make for bad days. Any contingency that requires you to be sharp in order to use it is not really a contingency.