Leaving a company is a massive milestone. Whether it was a personal choice, a mutual decision, or a sudden layoff, the decision has been made and it is time to look at the next chapter in your life. Starting that new chapter always deserves acknowledgement and support.
In this gist you'll find resources that people have found useful to know about when transitioning companies.
Most companies give you a limited time to exercise your options after you leave the company (usually somewhere in the 90 day range.)