Thanks for your reply (and for not taking offense at my words)!

I haven't read any of the manifestos, either of the Christchurch shooter or this most recent one. There is, however, one terrorist's manifesto I consider to be part of the basic reading list of environmentalism. It's Industrial Society and its Future by Ted Kaczynski. And yes, he mentions all of these things, and more. Yet, I wouldn't say he is anywhere close to being a white supremacist. On the other hand, there is no reason why white supremacists should not go through the same reasoning process, only to arrive at their own conclusions.
Now, I may be completely off here, since I really have no interest in following the news on the regular mass-shootings in the US, but it seems to me that most didn't even have a manifesto. The ones who did, had something about their teenage angst, or sexual frustration. As I said, I can't back this up by any facts, it's just my impression. So while I agree that white supremacists are real and present, I don't think they are as formidable as your post makes them seem like. But please throw some facts at me, to correct me if I'm wrong.

Regarding going around with guns, civil war, and militias: Could you imagine the reaction of the state if these kinds of things keep happening (especially before election time next year)? I'd say increased police presence, militarized law enforcement, and a perpetual marshal law-like state (if not fully declared marshal law) seem very likely. Obviously, the far right is going to respond to it in its own way. As a result non-white people, and whites with different opinions will be the target. So why would these people not organize themselves into militias too? After all, the US still gives everyone the right to arm and organize themselves to ensure their protection, including from the state, if necessary. Sure, not everyone is going to want to fight, but I doubt people would willingly be put on trains en mase without resisting. In return, this will provoke even more backlash from the state, pouring even more fuel over the fire. So I don't think a civil war would be like the last one, the USA vs the CSA. It would resemble more like something we saw in Bosnia a few decades ago.
Finally, I believe food shortages and violence feed into each other, even without any underlying political, religious, or racial tensions. So preparing for one, necessitates the other.