I get what you are saying for a general spare or backup plan. But, if your phone is at the bottom of the lake how are you contacting your carrier?Keep that sim and a spare phone. When your phone disappears, (stolen, at the bottom of a lake, etc) , contact your carrier and let them know you need to move service to a new sim. within 20 mins you will be back in business on your old number.
I’m thinking about what I would do if in an emergency situation either myself or someone else needed help. How would I contact help. Assuming no cell phone because of mechanical failure, lost, in the lake. I would most likely try reaching out on 2m. After that I’m at a loss in my plans.