While farmers are worried about competing with cheap imports (eg v low animal 'welfare' standards meat from the US), I don't see how those imports can be all that cheap if they're being flown in.
None of it makes sense. We're better off importing things from the closest neighbours, by ship/lorry. You can't get fresh food from the US or Asia by ship, so it'll be immediately increasing pollution and costs.
The problems will come with importing fresh food, I think. While yes, technically lorries can still go back and forth across the channel, the legal paperwork won't be in place, so they're going to get stuck. Or, probably more likely, they're going to get waved through because the government doesn't want people to go hungry, and then that means the contents aren't being checked for quality at all.
But that's only at our end, if they do get waved through.
Fresh food/medicine supply problems do worry me. It's the worst time of the year to leave the EU, let alone have a No Deal, because we won't have the weather to grow our own crops at that point.
Combined with covid, the next few months don't look like fun. Hopefully they'll manage to get things running after a few weeks, but we won't ever have such a wide range of cheap, good quality food again, unless we rejoin. (And even then, we won't have such a good deal as the one we left, because why would all the other countries be happy for that after all the disruption?).
It's depressing, but humans are adaptable, so hopefully we will find new ways of living with this. Maybe new, local farms will spring up, there'll be a lot of demand from those who can afford it for "EU standard" food without previously banned pesticides, and I imagine a huge number of people will turn vegetarian or vegan to avoid unlabelled meat. So things could end up fine, but it's just the amount of time it'll take in the meantime to get to that point.