This is the fifth (and last) book in the Hitch Hiker's Guide to the Galaxy series.

It's easy to become disheartened when your planet has been demolished for an unnecessary hyperspacial express route, the woman you love has vanished in a misunderstanding about the nature of space/time, the spaceship in which you are travelling crashed in flames on a remote and Bob-fearing planet, and all you have to fall back on are a few sandwich-making skills.