You kill Boomers? The lovely lovely people that are the Boomers? ;_;
On this level 39 character.......I kill
everyone.

Nothing else to do but kill everyone. Where else would I get my XP to get to level 40? That's probably the reason why I'm still 39, I don't kill enough.
I've already killed: The Fort, Camp Golf (that was extremely hard), Camp Mccaran, Nellis AFB, Red Rock Canyon, All the Powder Gangers in the Mojave Wasteland except the Vault 19 ones, CW Cove, The Kings, Almost the Strip (I just can't kill the only safe (yeah, right) place in the Mojave Wasteland, and some other places I can't remember.