How to unlock missions and other items:
Missions A-2 to A-4: complete mission A-1
Missions B-2 to B-4: complete mission B-1
AUV: complete mission A-9
Dragon-SPL car: complete mission A-1
Super car: complete mission B-1
Tank-90: complete mission B-8
Tiger-SPL: complete mission A-8
Yakuza car: complete mission B-9
Music test: complete all twenty missions to unlock the "Music Test" selection at the options screen