Some useful references are collected in this post and this would be kept updated if necessary.
List of mathematical symbols
Detexify–A handwritten symbol recognition: you draw it and they recognize what it is
templates for optimization models
table generator: one of my favorite online service helps you rapidly generate your table and realize the corresponding scripts
Over 2400 templates from overleaf: Overleaf is an online collaborative LaTeX editor with integrated real-time preview.
Over 400 templates from Sharelatex