[quote name='cthomer5000']Anything that shows up in your library when you play RB2 will be in your Blitz library when you play it.
Blitz tracks are automatically in RB3... everything except the on-disc RB3 tracks are automatically in Blitz.
Make sense?[/QUOTE]
This is assuming you've exported the RB2 content. Anything NOT on the RB2 track list that shows up in RB2 will show up in Blitz with nothing extra (like track packs, individual DLC tracks, RBN, green day, lego, etc). You will have to pay the fee to export RB2 to play the RB2 songs in Blitz. Songs exported from Blitz will NOT show up in RB2 but WILL show up in RB3.
Edit: Also, if you're an achievement, junkie, beware that there is an achievement in blitz for playing 300 different songs, as well as one for playing one from each decade from the 50's. There are only a half dozen songs from the 50's, mostly johnny cash so you will probably have to buy a song for that cheeve.
PPS: If you're concerned about having friends to challenge on blitz, you can attach your RB blitz info / gamertag to your facebook profile and any of your facebook friends, regardless of their platform, that have played blitz will automatically show up in your score feed for each song they've played. There's also a pretty nifty set of quests in the FB app that get you a ton more coins for power ups, which is the hardest thing to get when you're just starting out.