You are going to love the K-5. As for an "all around" lens for trips, let me tell you my experience. A couple of years ago, I bought the Pentax 18-250mm, thinking it would cover just about anything (it's still available on the used market). Indeed it does cover a wide range, but with a couple of downsides. First, it's heavy, adding very noticeable weight to the camera. When you're lugging this combination around, I guarantee you'll feel it. Secondly, this lens exhibits "lens creep." When it's not locked into the 18mm position, when pointed down or up, the lens will telescope out or in. Ya gotta keep a grip on the zoom ring to prevent this. It's an annoyance. Also, this lens is NOT weather resistant like the camera.
My wife and I were about to take a trip to Hawaii, and I wanted something better for an "all around" that I could "walk around." After looking at all the options, I decided to buy the Pentax 18-135mmWR. Now I had something. It's MUCH lighter than the 18-250mm, has no lens creep, and is weather resistant. Its zoom range is more than adequate for about 90% of the situations you will encounter. Not much bulkier than the kit 18-55mmWR lens, but way more versatile. It's not a particularly fast lens (much like the kit lens), but with the K-5's tremendous ISO range, it's not a big concern. Also since the K-5 will give you big 16.2 MP pictures, you can still do a sizable crop to give you the equivalent of a lens with longer reach.
I took the K-5 with this ONE lens to Hawaii, packed in a pouch with a spare battery and memory cards. I left the battery charger in the hotel room for overnight charging and rotated batteries. I had the perfect compact package, and since it rains every day in Hawaii, I didn't worry about water getting through the lens. This turned out to be the best decision I ever made, excluding getting the K-5 in the first place. Tremendously versatile, light weight, and weather resistant to boot. Once in a while I wished for more reach, but the reduced weight more than made up for that small limitation compared to the 18-250mm. What follows are some representative shots taken in Hawaii: