I shoot a lot of concerts and festivals, most being at night, and flash photography is usually a big no no. Even with a press pass flashes are largely looked down upon. Remember you are still there for their performance, they arent there for yours, so be considerate to both the band and the audience. Shoving your way through a crowd isnt going to get you anywhere, always be polite and people will be a lot more willing to let you through to get your shots. Once and if theyve let you through dont stay long get your shots and get back out. The 50mm 1.4 rarely leaves my camera, but my 24-70 2.8 is always in my bag. A good wide angle such as the 16-35 2.8 is always nice to have also. Most of these lenses are good if you can get fairly close, if you cant get a press pass or you just cant get to where you want, instead of a good zoom like the 70-200 2.8 USM IS, I tend to use the 135 2.0 a lot more, its a super sharp lens with a super quick AF but you have to do a lot of moving to get your shot. Good luck with your concerts, its a very tricky type of photography but also when you get the hang of it and get good connections its also very rewarding!