Post Its Notes are one of the most useful things during the first two years of med school when you have to orient yourself in 300 pages. The page markers are definitely must if you are not a note taker. Otherwise various sizes of post its notes in multiple colors will make your life much easier. I heard one of my classmates annotating the entire path review book onto another one with post it notes. I know that is little extreme, but the point is you can do a lot with them.
Colored pens are really useful when you go over notes multiple times, so you can only concentrate on things that you need to without being distracted by information you already know. I personally prefer the Muji ballpoint multiples, because they don't bleed. But if you are more of a gel point person, then G2 ones are easily accessible. I personally think they bleed and make messes. But with simple circling and underlining, I think they can get the job done.
I practically ate highlighters. I have tried different ones, but the only one that lasted longer than two days were the Sharpie Highlighters. You need bulks of them. I have a few different colors that I used sometimes. If you are color coder like some of my classmates, then having bunch of them will be pretty useful. Just make sure to learn which ones will show up over the other if you are planning on highlighting over.
I take notes in my own words when I have to understand more complicated topics, then I exclusively review my notes afterwards for the exam. For these kinds of notes, I can be little OCD, wanting everything to be neat and organized. I prefer clean performance without much of an effort. It is hard to work with pen that requires tons of effort when you have to write all day. Pilot Acroball Ballpoint Pens are pretty awesome. It is more like a gel pen though without all the bleeding.
I used to be a such a huge fan of mechanical pencils. If you think all mechanical pencils are made the same, think again. Paper Mate ones are the best. They fit really within the hand and have amazing back erasers that are replaceable. They are on the pricier sides, but if you prefer the disposable ones in packs, then these BIC ones are good.
Ear plugs or noise cancelling head phones are must. Being on top of your game every day every week every month for 2 years is hard. You really need these guys to cancel out the distractions around you. Ear plugs are cheap, but if you are more of music person, then I highly recommend Dr.Dre Studio Headphones. Dr. Dre Solo versions with or without wires are just as good, but they are too small for my ears, which hurt them after couple hours. I thought regular headphones will do the job, but honestly once I tried my husbands Dr.Dre headphones, I was hooked. I wish I invested in them from the get go.