Always write shit down, y'all.
It came up for us today because my husband's coworker (the only other person in his region in the same role as him) was fired today. This person is negotiating a severance package using the records they kept.
I've told my husband to document every additional task he takes on in their absence, because they don't plan on replacing this person (also, fuck that), because he needs to negotiate a pay increase.
Document everything. Keep a fucking work journal, e-mailing your personal account from your work account with any important daily details, such as incidents, additional work you did, coworker layoffs, etc. Keep it in a folder kr give it a label so that it's easy to go through later.
This probably sounds excessive, but I assure you it's not.