Overnight bag
un baise-en-ville = overnight bag (slang)
from:
la baise = screwing (or any other synonym you can think of)
la ville = city
the meaning, clearly, being that the bag contains all you need to have an overnight affair (in the city).
Note that the use of baiser requires attention, as it means both to kiss and to screw, although nowadays it tends to lean towards the latter.
Labels: french word bag baiser