When I travel for work or for a family vacation (ie, any trip that is not explicitly dedicated to photography), I take either the 4x5 Crown Graphic with standard 135mm lens and a handful of film holders, or an old 6x9 folder. That's it!

EDIT: my avatar is a photo of me with a Crown Graphic on the Galapagos Islands....yes, I photographed the Galapagos with only a 4x5 Crown Graphic, ten film holders, a changing bag and LOTS of film!