As a past guest with a past guest number (you can get that by calling Carnival). You get an invite to the past guest cocktail party.We have never received a gift basket as a past guest. I agree with the previous poster it was probably from the Travel Agent (TA).
My last cruise was booked with a Travel Agent and there were thank you chocolate covered strawberries and champange as a thank you. Different TAs do different things as a thank you.