Does my Bitcoin-Qt wallet backup file have "everything" I need (private key)? Does my Bitcoin-Qt wallet backup file have "everything" I need (private key)?

I mean, is that the file I would copy and store offsite in case my house burns down? Does it have my private key encoded in there?
Your bitcoin.dat file contains your private key(s) as well, however I would suggest you extract them now for the addresses that hold money (if any), if empty then it's not much of a use, unless you accept donations there or have a business set up to that address. 

How to extract your private keys for addresses that hold at least some money:


Go to Help > Debug > Console
Unlock your wallet if it is encrypted by calling: walletpassphrase YOURPASSWORD
Call listreceivedbyaddress to get all not-empty addresses
For each of them call the dumpprivkey MYADDRESS
Call walletlock once you're through to lock back your wallet