Other
A collection of links to resources and tools which I have found helpful over the years.
Useful Tools
Detexify (Forgot the LaTeX command for that symbol?) : http://detexify.kirelabs.org/classify.html
SeeK-Path (Hand calculate k-space paths no more) : https://www.materialscloud.org/work/tools/seekpath
Wolfram|Alpha (Needs no introduction) : http://www.wolframalpha.com/
SymPy Gamma (An interesting alternative): http://gamma.sympy.org/
Quantum Espresso (Convenient, well documented DFT software) : https://www.quantum-espresso.org/
JDFTx (An alternative, well documented DFT package) : http://jdftx.org/index.html
Chroma.js (Generate and tweak colorscales) : https://gka.github.io/palettes/
Colorgorical (Need inspiration for a color palette?) : http://vrl.cs.brown.edu/color
Viz-Palette (Check how your figure colors will look to others) : https://projects.susielu.com/viz-palette
Resources
The LaTeX Wikibook : https://en.wikibooks.org/wiki/LaTeX
The Feynman Lectures on Physics : http://www.feynmanlectures.caltech.edu/
The Oxford Solid State Basics : https://podcasts.ox.ac.uk/series/oxford-solid-state-basics
The Materials Project : https://next-gen.materialsproject.org/
The legendary lecture notes of Prof. Daniel Arovas: https://phys.libretexts.org/Under_Construction/Arovas_Texts
Welcome Distractions
Project Euler: https://projecteuler.net/
XKCD: http://xkcd.com/
What If?: http://what-if.xkcd.com/
PhD Comics: http://phdcomics.com/comics.php