I would think complex nonfiction would have some memory benefits.
I'm not sure if there is a formal study on this, but I'm pretty sure that writing fiction must also be good brain stimulation.
On a slightly less literary note, some herbal supplements may be helpful. I'm currently using one I got from Amazon that includes "Ginkgo biloba, Bacopa monnieri, Turmeric, Phosphatidylserine, Gotu kola, Sage, Ashwagandha."
Because I wasn't having pronounced memory issues to begin with, it's hard to tell how much effect this particular combination has, but I do have no definite difference to report. My first cataract surgery occurred before I started taking it. My second occurred afterwards. In both cases, I was sedated for the operation. Memories tend to be more ephemeral under sedation (a little like dream memories in that regard). After the first one, shortly after the procedure ended, I remembered that I'd had the procedure, but I retained no details at all. The second time, I remembered every single detail. They did fade pretty quickly after that, but I held on to a lot more initially. So I figure that has to mean something.
Physical activity is good, too. Reading and writing are both sedentary activities, so it's good to mix in some physical stuff. I take an early morning walk every day for an hour (except in the rain) or when my schedule is really pressed. I have different routes, so it doesn't get boring. It's also possible to listen to audio books on a walk or throw writing ideas around in your head, depending on where you are. (In some settings, you might need to be a little more vigilant.) I'm in a suburb of Los Angeles, but we now have wildlife because the original habitats were destroyed. The wild rabbits I don't have to worry about. Wild skunks I have to be able to dodge. The coyotes don't seem interested in attacking a full-grown human, but I don't get too close, anyway. (Mostly, the people who need to worry about coyotes are people walking their dogs, particularly small ones. Coyotes will follow people a long way if they think they can get a canine snack out of it.)