ZDoomsday Electronics
What electronics will be usable when/if the power grid goes out? How about 10,20,50,100 years later?
Usable Electronics
Crystal Radios, if they can be kept in working order (away from rust, corrosion, and oxidization), will work without any power. This gives you access to some range of AM radio. Hopefully someone with a working transmitter will be sending something out where you are...
Analog Multimeters, will work in all but the resistance mode (which requires batteries).
Practical Concerns
Rust
Any metal that is exposed to long term temperature and humidity differentials (which will be almost everywhere when the HVAC no longer works), will rust over a period of decades. Indoors or not, it doesn't matter. You don't need rain for rust.
Moving Mechanical Parts
If you don't have the ability to replace parts, then pretty much anything that moves is subject to quickly wear and tear or breakdown after a short period. There are a number of hand cranked radios in https://en.wikipedia.org/wiki/Human-powered_equipment but that approach seems flawed.
Conclusion
It is looking like everything is going to rust, and become unusable, without power. More research needed.
