I can't believe nobody else noticed this, but when they are loading that car that Jack and Rose "had fun in", there are no roses in the vases. but when they are about to, "have fun" there is clearly a rose, Rose even turns to look at it!
That’s true, Rose did look at it, but when they were loading the car, far shot of the exterior was shown; flower, on the other hand, was in the interior of the car when Jack helped her in, remember…
Considering a considerable amount of time had passed between the car being loaded, and the steamy sex scene (at least a full day, maybe two??) is it just possible that somebody might have visited the car, during that time, to place the roses there? Highly unlikely, definitely, but still possible.