Congratulations!! As far as I am concerned, you’ve made it to the finish line in your child rearing journey, so be sure to celebrate yourself in a big way. Do something nice for yourself! Treat yourself with something special.
I would definitely make a list of things you enjoy, preferably inexpensive that can be done semi-regularly, and start mapping out what day to day life would look like. If you aren’t a gran just yet, it’a great to start filling up your life with activities and interests now that do not revolve around grandchildren, adult sons and daughters. Too many get over involved and over-invested and it can be stressful for various reasons. This way, you can just enjoy them without the complicated baggage of being too in the mix, and therefore dependent on them for fulfillment in your later years.