For bags I recently got the Think Tank Retrospective 7, which IMO is the greatest mid-sized camera bag ever made. And the best part is, you don't look like you are walking around with camera gear. I put two lenses, my camera, a flash, spare cards, ND filters, stepper rings, radio triggers, lens pens, a few small light modifiers, cables, chargers, and my iPad in that thing.
Flash: Everyone needs a real strobe. The ability to use the IR controls on the 7D to fire off-camera flash open up a whole world of possibilities. Start with IR control and then grow from there. Once you get a flash, you'll have no trouble finding ways to spend money on light modifiers (umbrellas, soft boxes, etc. etc.) and more and more flashes, not to mention radio-control.
+1 lots of my equipment is in the form of flashes and light modifiers. They can really make a difference, even more than a lens in some cases - look-up "strobist" and you'll find tons of cool stuff you can do with flashes. Best part is if you get some manual flashes, cheap radio triggers, cheap light modifiers, and some gels, it can actually be much less than the cost of some lenses to get a near professional level lighting setup. Although I'd start with a 430EX II, and maybe a cheap umbrella + stand kit for like $60, and see how you like it.
I think most of the good lenses have already been mentioned. If you aren't going full frame the 10-22mm is great on crop. The 24-105mm f/4 is nice on crop, but more practical on FF unless you plan to take the 10-22mm with you as well. The 100mm f/2.8L Macro is outstanding on crop and FF. The 70-200mm f/4 or f/2.8 lenses are also a good option, but only if you are shooting things at a long distance - closer in on crop camera they'll be hard to use.
And my two cents on the now endless 7D/6D/5D3 debate. If you are shooting subjects that move quickly, the 7D and 5D3 are the best options. The 6D however has an excellent IQ to price ratio, if you don't shoot fast moving subjects, it's a way to save some money, possibly for a lens or other cool gear - while keeping IQ at the level of the 5D3.
Also a tripod is a really important thing to have. I don't travel anywhere without a good tripod, there are just so many times they make the difference between getting a shot, and not getting a shot. Any old tripod will do the job 99% of the time, but the higher end ones will last much longer.