I escaped the Reddit regime a little while ago. I consider myself a marxist-leninist-MZT. Vegetarian and vegan for a few years. I've a lot of thoughts on how marxism and veganism are connected. Never wrote them down. I'd like to start smth like a club for marxist vegans to develop our own proletarian theory. Most vegan theory I found is either openly bourgeois (Francione is a literal TERF) or revisionist (anti-China, anarchist, libertarian). How about fixing this?
The issue you might be missing is that without capitalist agriculture and fishing, all those staple foods you're talking about will become much less available. You seem to be claiming that you need animal products at every meal. That is not an anti-capitalist position.
People will still be able to have some meat, fish, milk, etc, but not nearly to the extent that they do now. There will not be enough to consume it at every meal. That was the case before industrial capitalist farming, too. Maybe meat can be grown in labs but for now that's science fiction.
Industrial farming is a huge contributor to climate change and the sheer amount of land needed to produce so much meat and dairy is unsustainable. There is no future for humans if they continue to rely on animal products to the extent they currently do.
Arguments about the necessity of regularly eating meat, fish, eggs, and milk due to humans being omnivores fall flat. There will be some availability but the end of capitalism ultimately means your diet must become substantially vegan.
If humans can't survive that because they have traditionally eaten meat, then humans can't survive. The planet will become uninhabitable because of it.
This does not mean that everyone must become vegan. It does mean that most people will have to substantially alter their relationship to animal products.
System change will mean that diet is no longer an individual choice in the way that it is today so you don't have to worry about that.
We ate meat before capitalism was a concept and we did it since the cave times for hundreds of thousands of years and it didn't destroy humanity. You cannot delete carnivores from the planet or change the diet omnivores. It's nothing to climate when compared with fossil fuels coal, oil and gas, which guess what are also used to transport certain plants from other countries and thus wrosening the climate.
We'll fish and consume livestock and eggs regularly as we did always unless meat starts getting cloned which as you said, is not possible currently, simple as.