Baring some never-before-seen financial catastrophe of historic preportions, I don't need to earn another dime to live a comfortable and enjoyable retirement.
If I had more money, I could use it to advantage. I could have a lot of fun with another $1M or $10M or . . .
I do some volunteer activities. I enjoy working with the kind of people who volunteer for worthy projects. I could spend my time hiking or camping instead. And I do sometimes. But I also enjoy the volunteer activities.
I also do some activities I refer to as "nearly volunteer" activities. For example, I work on the election board during elections in Arizona. The county pays me for the 14 hour day I put in running a polling place. They pay me about $100.
But I really enjoy this work. I think it's important and I find it satisfying. I like the people who work with me -- a greatly diverse group of people. And I get to meet and talk with all my neighbors when they show up to vote. I could spend my time hiking or camping instead. And I do sometimes. But I also enjoy the nearly volunteer activities.
I still participate in a lot of professional/publishing activities. I have been a volunteer reviewer for several technical journals for more than two decades. This work pays nothing, but I enjoy it and it takes very little time. I've also been serving as a book reviewer for several technical publishing companies for about the same amount of time. They do pay me for this service (~$500 per book). I typically review one or two books per year and I enjoy it. I can do this work at my convenience or I can say no to the request. It's easy and enjoyable for me. I would end up reading most of the books I review sooner or later anyway. This way, I get to improve them when I read them. :
I get several offers each month to help some engineers do something that is both easy and satisfying for me. If I accepted all the offers, I would be working 60 hours per week. I could work an average of about 15 hours a week on these kinds of projects and make more money than I spend in a year. That's more time than I want to spend, but I take some of these jobs. If they're not fun, I quit.