First: thank you to everyone who continues to give advice! I'm still going to study (sorry most of you, I know you're trying to save me from myself), and I'll definitely take the 'big picture' approach for most things. I do have lots of reasons for wanting to study for the next few months, and some of those reasons have nothing to do with wanting to be prepared for vet school - I don't really want to explain, but please know that I'm not just discarding most of the advice here out of hand!
Second: a question that may be silly. Do most people forget details they've really learned within a few months? I'm from a family that plays lots of memory games/values memory/does lots of theatre and other performing arts/pushes getting lasting value out of every academic experience, so maybe I'm just really strange? But I remember a lot of the details I re-learned just over a year ago when I was studying for the bio GRE. I still remember most of the definitions on my flashcards and such. I only studied for that for about 10 weeks, and I really do remember a lot of that, despite not studying it since then. My mom and dad and sister (and my SO, now that I think of it) do this sort of thing too... is it really unusual? Sorry if this is a silly question! I haven't talked to many people about how long they remember stuff. 😕
I don't think it's too unusual, no. I memorized every dog breed and could apply that knowledge soon after receiving my first dog breed book at 6. I have since memorized cat breeds. I am able to expand on this knowledge to discuss most temperaments, grooming and exercise needs, etc. and could do this at a very young age. This didn't take me very long to do, but I was interested in it. Ask me anything about Jung, Freud, Rogers, various forms of therapies, etc. and I'd probably be able to give you an answer or at least an opinion based off of what I remember from the last four years. It might not be down to the exact detail of Freud used a silver spoon to stir his coffee in his book on dream interpretation, but I understand it conceptually. And then there are subjects people are just good at.
😛 I enjoy math but I don't study it for a hobby, and yet I pick it up quickly and remember how to go through math problems even though my last math was in 2009. While I'm sure memory games help, I also think that when you study something, you retain it. It's not always conscious material, but it's oftentimes something you can access. And if you remember most of it and feel confident about it, then you've already got the basics that everyone's telling you to have down covered. So I don't think it's unusual. What people are telling you is that it won't be of use to vet school, when you're going to have to work a bit harder and find new strategies because vet school is 10x the amount of what you've been learning.
For question one, since it's not about wanting to be prepared for vet school, what are some things that you want to study/learn that aren't vet school related? Do you like language or maybe you enjoy the performing arts? Maybe you could do a theater class or get involved in a community theater and work to be a part of a summer production? Maybe you could tutor or volunteer or give back to your community in a way that still allows you to study math, science, etc. through teaching other people? Because as people have been saying, there's nothing you can study, other than perhaps the bare basics you seem to already have down, that will prepare you for the sheer volume of vet school. Though I apply next year, I've been told that attending vet school is like going from the semester system to the quarter system to having the information you learn in each quarter packed down into one or two weeks of lecture at vet school.

The only other thing I can recommend to you is that you study how to study. Don't get too confident in "I retain everything" or "I have a good memory." Don't get too chuffed because you remember so much of your undergrad years. I actually plan on brushing up on my study skills before vet school because I'm one of those annoying people that does pretty well with minimal studying, and I know that this is going to effect me in vet school when there's too much information to roll my eyes up into my head, think back to the lecture and quickly scan it for the necessary information. Studying study skills wouldn't hurt you either, and there are so many tips and tricks that you might even learn something you didn't know before. I think the worst thing we can do is assume we're at a point we don't need to continue learning because of x, y or z.
🙂 But if you want to study something academic, I suggest studying something non-vet school related that's still of interest to you, since you said this isn't about being prepared for vet school.