When you consent to the search, you aren't limiting the extent of the search. Perhaps some day you will have the opportunity to try to put the back seat of your car back in, and you will change your mind.
Parting words from the LEO...Have a nice day.
Or, maybe reassemble the entire interior, reinstall hub caps, reload trunk (including spare tire), forgive the body search, and say 'yes sir' a lot.
Probable cause?
"Too young to drive a Thunderbird".
[Arkansas, and another reason I won't vote for Huckabee...but I've still got the T-Bird.]