Masks only afford minimal protection for you and some protection for others.  They do not prevent the spread by touching surfaces.  How long the virus remains on various surfaces remains uncertain but it is more than a few minutes. So, even if a store is empty, by opening the door and touching various objects in the store, the chances of picking up virus is not small.  Also, the quantity of virus (innoculum) can change the severity of the infection, just like more warriors can invade more than less warriors. Similarly, the more your immune system has its warriors properly armed, the better the chance of fighting the virus.

How to Make Your Own Face Mask at Home1

How to Sew a Face Mask – The New York Times

My Advice on Masks for Coronavirus _ MyHealth Beijing

1910.134 App B-1 – User Seal Check Procedures (Mandatory). _ Occupational Safety and Health Administration