Pears Cyclopaedia is one i grew up with. It was a tiny book with ~1000 tissue paper thin pages that seemed to always have everything i needed. From logarithmic tables and maths/physics functions to a periodic table.

I went to school before wikipedia and this book helped a lot.

https://en.wikipedia.org/wiki/Pears%27_Cyclopaedia

One of the greatest signs of human progress is that now we know enough facts to fill our pocket almanacs with them instead of making up prognostications.

I think the most meta-thing here is instead of using almanacs, we’re here linking to a Wikipedia article on a pocket reference.