This is a question that comes up time and time again. When we have a new camera, or lens and we're going away, we want to take everything with us, in case of this, in case of that, but after lugging around a heavy bag that dictates your trip, it can become tiring, frustrating and it can dominate your attention.
Things have changed with the growth of the mirrorless cameras, which are wonderful, offering the same quality in a much smaller package, albeit that the usability is not quite the same as a DSLR, in my opinion, but nothing that is not easy to get used to.
However, the science behind lenses remains the same, they cannot be downsized, unless the sensor is smaller, as is the case with micro four thirds or the Nikon 1 CX sensor, or if the lenses are smaller and therefore allow in less light.
Personally, speaking as Nikon user, I have had several standard zoom lenses, from the heavy Tank that is the 17-55 f/2.8, to the Sigma 17-50 f/2.8 (which I prefer as it is smaller, it has OS and quality is comparable) but I have also used the Nikon 18-70 f/3.5-4.5 which is a good quality lens in a small light package, with just a little more reach than the other standard zooms.
I feel that a good standard zoom, along with a standard prime, be that a 35mm or 50mm depending on the sensor size is the way to go. Even a DSLR shrinks in size and weight when it is fitted with a lightweight fast prime.
Ultimately, the object is to be able to enjoy your trip, to have the means to capture high quality images and yet still only have a small light bag on your shoulder that will not become a ball and chain.