FWIW, if the Tower says '[call sign] runway ## cleared for takeoff' and you say 'runway ## [call sign]' you have established two way radio communications and are good to go even if you have had no previous conversations with CD or Ground about it. Or whether or not the Tower gave you a squawk, heading, altitude or any other instruction. Is it ever going to happen this way? Nah. But like
@flyingron said above, different places do things differently and ATIS usually gives you the game plan on how they do it there. I'm of course talkin C here, not B.