Metal working can be a lot of fun. Iron, copper, aluminum, and other metals will be available in abundance. Copper (power lines anyone?) is very mailable and can be melted at relatively low temperatures. Aluminum is also easy to work, and should be easy to find. Iron is harder to work, but can be successfully forged with charcoal. I recommend practicing with either coal or a gas-powered forge before using charcoal. The real problem I’ve had with using charcoal is getting the piece uniformly heated, if you don’t the piece will have weak spots. Being able to overcome the low temperature and other limitations of charcoal is a matter of practice and experience, which are easier to get at higher temperatures.
One trick of making the piece cool well and evenly is first, do not quench the piece the last time. When you’re ready to cool it for real put it in a bucket of salt (modern metal workers use other chemicals, but salt is traditional). This slows the cooling process from hours to days, helping to prevent cracks and weak spots guaranteed to ruin your product.
Also, different temperatures give the iron different properties in terms of hardness. You can measure temperature by color or time in the fire, which was once measured using song (history of technology is fun).
No technology is inherently unsustainable, and if we are clever enough to redevelop our toys into sustainable technologies then there is no reason we shouldn’t enjoy the fruits of our species intellectual endeavors.
Electricity is easy to generate if you have copper. And I’ve already figured out air conditioning/refrigeration.
