I own and love this game, but Ben is right, it certainly has frustrating issues featuring. For one, its true, buying one item from the dealer at a time is little more than annoying.
The helicopter can deliver us full sized motors. Would it really be pushing the space to carry more than one item of stock at a time?
Also, a gripe Ben didn't mention, who designed the aircraft controls? I can pilot helicopters, no problem. The other aircraft though, hate me and now I hate any race or mission that involves them.
Despite that though it really is fun to play. Blow up so much stuff, it's great!