financial strength of a country - best indicators

You're on the right tract; do some research on the areas you have mentioned.
I would also add interest rate and stability of the government as important components. Good luck.

Thank you very much for your reply!
My problem is that there are a lot of indicators one could use (as I mentioned: savings, debt, reserves, GDP/capita, cash surplus or deficit etc.), but it is not clear what exactly their meaning / relevance is when it comes to assessing a country's financial strength (e.g., the national debt of the U.S. is enormous, but I doubt that this would impair the country's ability to respond to natural disasters in terms of financing the recovery) - so I would be happy about any suggestions on how to prioritize or weigh the indicators.

Best,
mella

All that, and take a look at power generation. It's hard to hide and gives strong clues to the current state of the economy. Of course, it predicts exactly nothing.

The problem with trying to tie down an answer with so many variables that influences any economy, all one can do is to provide an 'example' country to analyze how it will perform. Even then, it's an impossible task because economies continue to remain in flux that changes the character of any one countries performance.
Try to approach it with the country's GDP (strength of the per capita economy), the variety of products and services produced, interest rate, the social benefits of the country, the stability of its government, and how it can attract outside investments.
How any country can survive natural disasters is a very different scenario.