If it still does the job, there's no need to replace whatever-it-is.

I'm still using a solar powered hexalator (calculator that can switch between bases 2, 8, 10, and 16) that's old enough that the batteries won't hold a charge when there isn't a light shining on it. Got it in the mid 80s. It's still functional; useful for figuring out bit flags - so I'm still holding onto it.

I'm not sure tools qualify here, but I've got SnapOn and Ingersoll tools from the 70s and an oscilloscope and soldering station out of the late 60s.