The following is a list of checklists provided by various organizations to help people interested in accessibility keep track of tasks.
A simplification of the WCAG 2 standards for web accessibility provided by one of the most trusted voices in the field, WebAIM. Also incorporates the new criteria added in WCAG 2.1.
A collection of guides offered by the Department of Health and Human Services that include both PDF files and web accessibility.
The University of Washington has been offering guidance and resources on accessibility for many years, and this checklist covers the POUR (Perceivable, Operable, Understandable, and Robust) principle embraced by WCAG, with links for explanations.