Much obliged means that whatever was done is appreciated. Literally, it could be extended to mean that the person that says "Much obliged" now owes the other a favor. That the one that is obliged is under an obligation to pay back. Most people wouldn't expect a return favor though.
If a man is given a ride into town, when he gets out of the car, he might say "Much obliged". That would mean: "thank you for the ride. I am appreciative"
Nickname given to bales of marijuana thrown overboard or out of airplanes. Origin is reportedly from members of the US Coast Guard in the area of Southern Florida.
"Base we've got some square groupers floating outside of Miami harbor."