Lets say you bought a t4i with the kit lens? Youll want
-2 16gb (or bigger) class 10 fancy cards
-an extra battery or so,
-a decent tripod ( i got a manfrotto 701 with old legs)
-a decent mic (rode makes nice mics)
-A stabilizer (homemade fig rig is easy and effective)
as far as lenses its up to you, buying cheap is frowned upon, but you gotta do what you gotta do. Popular lenses include...
-Canon 50mm 1.8
-Rokinon 8mm fish
-Tokina 11-16 wide
-canon 70-200 f.4
hope that helps a bit, just a couple things that are nice to have to get going. It will take awhile to build up your bag, but variety is nice nawmean?