An interesting customer base might be small communal organisations. At our local scouts troop I had a discussion with a friend, who is also in IT. His idea (not fleshed out) was to provide small local organizations with a stack of already configured open source software to support the typical needs of such organizations (like a wordpress website, a nextcloud for file storage and common calender, limesurvey for surveys and event registration, mailman3 for mailing lists,…). Depending on the needs you could sell the initial setup process (your personal work in setting up and skill transfer) or ongoing support. Though such organizations normally don’t have much money to give away. So probably its not really worth your time financially (though probably really appreciated in the community).
Though having cash is not enough. The stores also need to be able to accept cash without internet usage. I think we had a case in germany a few years ago, where some supermarkets could not sell anything, because the servers, to which the local payment system connected (also uses for cash) didn’t work. Not sure, if that was because of a security incident.