There's more risk of harm from feeling falsly protected by a damp, ill fitting, poor quality mask that you've been fidgeting around with or reusing.
I've been using a sweat band on my wrist to rub on my face instead of my hands, and sanitise on entering and leaving the shop then washing on getting home and after putting the shopping away.
I live in one of the early hotspots, where it will have been spreading around at the point where it was a struggle to buy sufficient food during panic buying, and going into town to settle errands before any potential lockdown. That was by far the riskiest phase, but I got through it without consequence.
It was suggested at a briefing earlier this week that although assymptomatic shedding is not risk-free, by far the greatest route for transmission is from close, prolonged contact with someone showing symptoms. They should not be in the supermarket anyway. If the supermarkets were that awful for spreading, how have the supermarket workers not all been off ill, plus they don't have PPE and reluable 2m distancing.