One thing I kind of wish that I had done before hand is paid more attention to the Anesthesia flow sheets on my ICU patients. (If your hospital has flowsheets) It will give you a good idea of the drugs that they are using, and in what dosages. You can research them on your own from there. Also it might give a little insight into the things that anesthesia is responsible for that you wouldn't necessarily think of. You might be able to get a little bit familiar with some of the extra monitoring going on in the OR, like end tidal gasses, CO2, Train of four (you may already be using this, depending on your ICU), BIS monitors, etc. If you just kind of look over the flowsheets you might come away with a few concepts that you want to read up about on your own.
I also think it might be helpful to review the development of an action potential if its been a while since you looked at cellular physiology. A lot of the foundations stuff will draw on this basic understanding. Its hard to understand HOW a drug works if you don't understand what is happening in the cell. Maybe also refresh yourself on the different adrenergic receptors, what each one does when it is stimulated, and which vasoactive drugs affect which receptors (alpha 1, 2, beta 1,2, dopaminergic, cholinergic). Be able to say Epinephrine acts on ______, ______, and _____ receptors.
You'll definitely get all of this information and more in school-- but you may have a little less studying to do when you start if you look it over now. I wouldn't get too crazy in to it. A solid understanding will you put you in a really good place when school starts. Besides all of that, I would definitely take a vacation, enjoy your life, and scratch a few things off of your bucket list. Take care of any of those things you've been wanting to do for a while, because you most likely won't be able to for the next 2.5-3 years.