1) A "booty call" originally meant a telephone call (often late at night, often when one or more people involved had been drinking) whose purpose was simply to get the receiver of the call to go meet the caller and make out or have sex. I guess now it could be a text message, MySpace message, whatever, and you could still refer to it as a "booty call". NB- "Booty" is a term for rear end.
2) My guess is that clams are a good example of a mindless creature, "without a care in the world", and, lacking the capacity to worry, you could say they're happy (although, I wouldn't). Younger generations typically wouldn't use this expression.