For those into electronics, should you need very small ferrite toroids, say to build inductors or prevent self oscillations by placing them on low power RF mosfet pins, old core memory spare toroids can be used for that, and they are dirt cheap on Ebay.
The computer I worked with in my first job was a PDP-8 with core memory. We upgraded it from 4K words to 8K words for ONLY $5000.
I picked up one of these at VCF East a few years ago. Neat stuff!