Imagine a hypothetical scenario where a world-wide component shortage coupled with a long-term global pandemic meant it might be decades (or never) between finding new/replacement computer parts.

What would you need (hardware, spare parts, tools etc) to make a computer system that would last as long as you did?

It doesn't need to run AAA games, just powerful enough to, say, play videos - and be reliable enough for developing software for a long long time.