Get some FABRIC plasters - they stick better. Mossie rep, brufen-type painkillers - any injuries are likely to be muscle strains. Diacalm in case of the Aztec Quickstep. vaseline in case of chapped thighs etc, lipbalm too.
Resolve, to clear up your hangover.
Thats about it really. Ensure you take a sense of humour.
1. Vaseline (I don't know what the new webbing is like, we had '58 pattern and the nipple injuries were like something out of a bad snuff movie after the CFT).
2. Brufen (or Nurofen Plus, same deal. I took a mate's buckshee migraine medication: Bad Boy!).
3. Tubigrip-style bandages for ankles/ knees etc. Even if you don't need 'em, someone else will and your Good Egg quotient will rise accordingly.
Seeing as I have epic chalfonts, I also took three litres of Preparation 'H' in old Pepsi bottles (I didn't need much of it, so the rest got used for all sorts of tomfoolery). And a lucky rabbit's foot. I also took a load of Pro-Plus and a bottle of Scotch, but whatever gets you through the night...
The Doctor will sort you out with anything else if you pick up an injury, which hopefully you will not.
Second all the above, esp the zinc tape (essential if you're wearing CAB).
A good trick of mine is to soak a little cotton wool in surgical spirit and wrap it round a sterilised needle. Now put the cotton wool in a little sealable bag (like a freezer bag or a bag like some plasters come in) and put it in your FA kit, although obviously you'll need to be using a solid kit otherwise it'll get sqaushed and won't work.
Now, if and when you get blisters you can just yank out your clean needle, burst the wee fecker, dab on some of the surgical spirit dry it and stick a plaster on it.
Echo they above but your probably going to do less athletic phys than you've done during your previous recruit training, so maybe base ur med kit on what u need at the mo. When I did mine I was a skinny 17 year old, my main problem was lack of food - I needed four square meals a day plus I wasn't used to the lack of sleep. Not sure about the use of proplus, maybe your storing up a problem for latter on.
The best piece of first aid kit I've ever seen was dioralyte (used for people with the shits), an excellent hangover cure (was on the dewpond run on accension islands when I tried it, sober as a judge after 3 miles and roaring to go)
I only used the Pro-Plus for the final exercise: I'd done CMS before and I knew it would be all bugging out, changing in and out of NBC kit and stagging on with about 3 hours kip. It was pretty handy for that.