Yeah, all the rumours point to them announcing the next design around the 11th of June - likely to see a thinner body, retina display but also the removal of the DVD drive, so if that's something you need you're probably better off waiting a while longer and buying one of the previous generation models for cheap.
I know what you mean, its pretty important when you're spending this kind of money! Well I suppose it depends how you're going to be using it - if its just going to be sitting on your desk then I don't think I'd bother buying anything (except maybe an external mouse/keyboard). However, for carrying it around you'll probably want some sort of case or bag. If you mean accessories or software you need for it to run out of the box though, you don't
need anything at all.
Personally though, I have these:
iWork - basically your OSX equivalent of Microsoft Office. Would definitely recommend it over buying Office.
Apple Care - if you're a student you can get this heavily discounted, and its really worth it in my opinion. For a 15" Pro, you have to fork out £60 for it with education discount, whereas without the discount its well over £200. Apple are great with repairs and often don't charge for a lot of things, but getting an extended warranty is probably a good idea when you're buying a £1k machine.
Hardshell case - just like any laptop/phone/etc there are a billion different cases you can get, but I've had one made by Incase for quite a while and I love it. I've not owned an actual sleeve or anything like that though, since I just put my lappy in my rucksack everyday (its got a built in slot thing).
Mini DisplayPort to HDMI - similar to cases, there are loads of companies that make accessories like this. Apple do their own, but its a lot more expensive. I don't own the one I linked to since I can't actually remember what brand/model it is, but they all do pretty much the same thing. Got it so that I can hook it up to my external monitor.
Overall though, just like anything designed by Apple, accessories are often more expensive than the standard brands and its something you get used to after a while. I'd definitely suggest you buy AppleCare, iWork and some sort of case though - you'd probably struggle without. Hope that answers your question somewhat, if you've got any others I'll still be here