I try to keep things light. I will pack a couple speedlights mounted on light stands, all rigged up with radio triggers and ready to go. I can easily carry two of these along with my camera (on a Black Rapid Strap) and my camera bag that holds a couple lenses/battery/cards/etc. Clients are almost always willing to help carry something too, although I never ask.
For me, this makes off camera lighting much more manageable in terms of setup time and carrying around equipment. Just put the light stands where I want them, fire a couple test shots, and away we go.
As far as scouting areas - it doesn't hurt. The best thing to do is try to go at the same time you anticipate photographing your client. This way you can get a better idea of what the lighting will be like when you come back. I used to scout before every session when we first started, but after doing this for several years I am confident enough in my ability to be able to assess a location on the spot, evaluate the light, and decide where I want to go without needing to scout ahead of time. (That doesn't mean scouting is for less experienced people -- it's just not a regular part of how we do things, that's all.)
If I have the luxury of an assistant, then I'll also use a portable light stick with a small softbox (and speedlight). This is an extremely versatile piece of equipment. There have also been times where I've brought my AB800's, large softboxes/umbrellas, battery pack (Vagabond), but those are not always practical in terms of setup time and needing an assistant to carry things around. They do give me more power and a better quality of light than my speedlights though.