This cartoon by Chappatte from The International New York Times relates to the floods which are currently devastating large areas of southern Britain. With nearly 6,000 homes and businesses flooded, this winter is expected to be the wettest on record. Read more >>
The cartoon shows a double-decker bus travelling through the flood waters somewhere in Britain (note the Union Jack flag). One of the passengers comments to another, "That's where the second deck comes handy."
If something comes handy (or more usually comes in handy), it is useful. • I think that this gadget will come in handy in the kitchen.
The bus in the cartoon is an old-fashioned Routemaster. In London these have now been largely withdrawn and replaced by more modern versions. Although they are still used on two 'heritage' routes, their days may be numbered.