If I was in your shoes, along with my K20D, I'd take along my Sigma 17-70 + my DA55-300, for sure. Between the 2, I would have moderately wide-angle to fairly long tele covered, which will work for me in almost any situation. The Sigma 17-70 also has a nice close up feature (1:2.3), which is great if you think you're going to want to shoot some of the local flowers along the way. Both can be had new for under $800 total.
If you'd rather stick with Pentax-branded lenses, then the DA16-45 is also a good option--nice IQ and a bit lighter in weight than the Sigma 17-70. Pricewise, it's in the same general ballpark as the 17-70. While a good bit more expensive, the DA17-70 is also worth looking at.
If I wanted something for handheld low light, I'd throw in the FA43; I think it would work well with the video of the K7, too.
If you've got the room, consider picking up a small tripod and ballhead. Along with a cable release, a tripod will help you improve the IQ of your images regardless of which lenses you use and will allow you to get some shots in low light that you wouldn't be able to do just handheld (think nighttime cityscapes); you'll be able to use ISO 100 + smaller apertures for greater depth of field no matter what the lighting situation.
HTH,
Heather