Can't help a great deal on KAF. This is more Bastion-specific unless stated for KAF.
The important stuff....
Smokes - cheapest are at the Danish PX, $20 fr 200. If you get lucky they'll have what you like, if not they're only $25 in the NAAFI. Avoid the US PX on LNK if you're a tabber, they're bloody expensive. In KAF they're even cheaper, think I was getting 200 marlboro lights for about 16 bucks there.
Driving - Make sure you have your FMT on you at all times, and that you are logged as a driver in the wagon you've got, and also make sure you've been to MT to get your FMT updated with whatever you need to drive (even having Tata 4x4 put on your FMT). The fuzz are starting to stop people and checking docs. Don't almost run over the MTO, that will get you a six month ban going by what happened on KAF a few weeks ago.
Kit - people are turning up without being issued their ballistic glasses, GET SOME, they are mandatory and on Bastion the only authorised eyewear I believe.
I think the desert rats type MTP hats are still frowned upon (possibly banned? Dunno, I never had one).
Don't buy foot powder from the NAAFI, get to the med centre and in the corner of the waiting room there's usually a load of Mycota for anyone to pick up. Don't take too many, we all need some.
Buy a hard drive online before you go, much cheaper than in the NAAFI etc.
MAKE SURE YOUR BOOTS FIT! - One of our lads last year got trench foot because he hadn't realised his boots were about 2 sizes too big, so was wearing 2-3 pairs of socks and his feet went rotten.
If you're gonna be running, make sure you wear your lumi belt, I believe torches might now be mandatory but nobody ever stopped me for not carrying one. Run AGAINST the traffic, that may be simple but seriously do it, there are some terrible drivers out there and I got clipped twice at night. If you're running towards them, you can at least see them. Running on the roads with headphones in is banned, but if you do it at night nobody will see.
Be careful though.
Best cookhouse by far is Bastion 3, they have some cracking theme nights too. Leatherneck is okay, especially if you like ice cream. You just have to sign in with your name and unit there. Lots of free cans of coke etc too.
You are not allowed to tailor your gardening hat, but the tailor will do it for you for about 15 dollars. Take your beret, you may need it.
There's probably more, but that's it from me.