I regularly travel overseas. My basic kit is an all-around zoom lens and a fast fifty. For your lens line-up, the DA18-135mm and 50mm f/1.7 sound the right setup. The all-around lens 18-135mm would be typically mounted all the time, with the fast fifty in your pocket, for evening and night time shooting.
There are trips where I know in advance that I need some specific lenses, but these are rare. For example, I shoot tidal bores in France and the bores arrive a sunset and sunrise: thus I choose accordingly my lenses with a short tele (FA77mm f1.8) and a longer lens (FA*300mm) + TC. Otherwise my default kit is DA18-250mm and Voigtlander Notkon 58mm f1.4.
By the way: you will be travelling in summer time, when the weather is dry. WR is not a 'must'.
To sum up: all-around lens + fast fifty is the best combo to travel light.
Hope that the comment will help.
Last edited by hcc; 06-23-2015 at 03:31 PM.