I just heard about the Classics Club in which people promise to read and blog about 50 classics from a list they devise themselves within five years. I signed up for the group on Goodreads even though I haven't yet created my list of 50 classics. I always have a hard time picking classics, even though years ago I wrote two bibliographies for Vermont librarians on this very topic. This point in my life is a good opportunity to read some books I have never read and always thought I should, and also to re-read some old favorites.
One of the resources for building the list of 50 books is a website called 100 Essential Reads for the Lifelong Learner, organized by broad topics and including history and biography along with fiction. I really should read more nonfiction and hope this activity leads me to do so. Another resource is called The Well-educated Mind which has some more unusual titles on it. I'm making a note of these lists here so I don't lose the links.
I think my personal list will be a mix from a number of resources and, probably, my own mental "wish I had read that" list. For example, a priest who used to read widely and came to the library frequently always recommended I Promesi Sposi. It's been on my "list" for nearly 40 years! I have never read Steinbeck's Of Mice and Men, nor have I read The Grapes of Wrath. Both seem appropriate for a lifetime reading list. When the list's ready, I'll publish it here.