I am already working on my side project which I plan to use more in retirement.
I just got licensed as a marriage officiant! I want to be a marriage officiant who performs intimate outdoor weddings - and I will hike, bike, ski, canoe, climb to anywhere you want to get married and right now I think I'm the only one in my entire mountain valley who does this for hire. I am working on my website right now. My H could help with either being a witness, provide guitar music if needed, or even taking photos, or just pour the champagne.
I don't care if it's cheesy, I really was looking for this exact thing when we were getting married.
We also considered doing AirBNB and renting out our basement. It's a huge daylight basement with 3 bedrooms and 1 bath, private entrance. You can select the weeks you want it open to the public, and hide weeks you are not around.
Campground hosts for national parks and forests. They pay a daily stipend and you'd live in your RV for a couple months.
I've also considered being a home inspector too.