For groups, couples and singles portraits a zoom is a nice convenience as it could also work very well for architecture, close-ups.
The 35-70mm f/2.8D AF, 28-70mm f/2.8D AF-S, 24-70mm f/2.8G AF-S are lenses frequently used for this.
I've also seen the 17-55mm -previously labeled the "photojournalists delight"- largely replaced by the 24-70mm. The latter has even better image quality -that is a lot to say- and almost none of the distortions of the 17-55, plus the longer focal length helps in many situations.
When traveling light a two-lens kit is best. When traveling very light, a single mid-range zoom is mostly preferred.
A reference has been made to weight on the neck. In my experience, photographers tend to misuse a camera strap. When on the neck, the camera is best to be cradled in one hand. Only alone in the neck on emergencies, when you need both hands for something else and not for long. The practice of just let it hang from the neck comes from an era when film bodies were small and usually carrying a very small lens. Not today.
If you are 'going about' for long and want both hands free it is best to use a sling strap, preferably one without metal parts than can mar your gear or worst, getting dislodged from the body.