If a solar flare powerful enough to destroy the entire electronic payment system were to occur I'm sure everyone will be fine with you buying your storable food and colloidal silver with cash.
But solar flares that powerful are an actual serious threat, and have been recorded throughout history. It's just we have been so lucky to develop a heavy dependence on electricity in a quiet period.
>In June 2013, a joint venture from researchers at Lloyd's of London and Atmospheric and Environmental Research (AER) in the US used data from the Carrington Event to estimate the cost of a similar event in the present to the US alone at US$600 billion to $2.6 trillion (equivalent to $698 billion to $3.02 trillion in 2021[28]),[3] which, at the time, equated to roughly 3.6 to 15.5 per cent of annual GDP.
NOAA currently puts Carrington Events at a 1 in 500 year occurrence on Earth.
