I am a skilled metallurgist and engineer and, like most well-educated people, I'm terrified by the possibility of an impending apocalypse. Let's not worry too much about what form it takes. Nuclear, ecological, cosmic - I mean we're spoiled for choice after all. The point is that it's going to be so catastrophic that civilization will collapse. Without systemic access to learning or the internet, people are going to be reduced to an iron age level of technology within a generation.
Now I want to prepare for this scenario not for myself or my family - no-one knows who's going to survive after all - but for humanity as a whole. I want to build and leave behind a whole bunch of stuff that we can make now, with modern technology, but which only requires a dark-age level of skill to operate. A basic example: an axe made of modern steel is going to be pretty valuable resource in a society that can only smelt crude iron.
Nowadays, we'd mostly rather use a chainsaw over an axe to cut wood on a grand scale. In the new iron age, though, that's not practical. Machines of any kind require a power source and/or have easily damaged moving parts. So we can't leave actual modern equipment like chainsaws behind for the survivors. Yet, surely, with all the skill and technology at our disposal, we can actually do better than a basic steel axe?
Of course I'm not really a skilled metallurgist or engineer. And this is my question: if you were going to re-design simple tools and weapons in this day and age to make them as useful and as long-lasting as possible, what would you do? What could be done with our titular axe to make it light and balanced, prevent rust, get (and keep) the keenest edge possible? What other sorts of tools might you leave, and what would you change to make them of maximum utility in our new iron age?
EDIT: I seem to have framed this question badly. My proposed metallurgist isn't in any way a protagonist in this scenario. It's just a framing device to ask the question of what objects might modern human purposefully leave for a future civilization rebuilding itself after total collapse. She will be long dead by the time people discover the things she has left for them.