Certainly medicines can easily be airlifted if needed, there is no problem there, quite a lot of tropical and out of season food is already air freight, many will have noticed it being loaded into returning holiday flights. Bananas from Carribean, Beans from Kenya, Grapes from South Africa.
Staple food, Bread, Meat, Milk are either largely home produced or imported from ROI and I will guarantee producers in Southern Ireland will want that to keep that moving. In a no deal scenario there will be some disruption of food that arrives on truck via Dover, so if you want Lettuce,Tomatoes or Aubergines in January you may well be disappointed.
So let's have no scaremongering, we are not going to starve, there are not UBoats sinking shipping, no blockade, essential supplies will get priority. I'm more concerned by the affect on jobs disruption will likely cause layoffs in many industries because their supplies don't arrive, you can't make cars without widgets.