I travel a lot for work, and one of objectives of my lens choices is to have a nice light, high image quality kit for travel.
When I am travelling I have my camera gear, laptop and associated cables etc in the Think Tank Shapeshifter bag. The bag has 5 internal neoprene pockets. Because Pentax prime lenses are generally small and light, and the K3 is relatively small for a DSLR I can fit 2 primes to a pocket and this generally allows me to travel with the K3 and a wide zoom mounted in one pocket, the HD 55-300 tele-zoom in another, and 4-5 additional primes in the remaining 3 pockets.
I also take a Crumpler 5 bag with me for shoulder day bag - which has room for the K3, 2 zooms, and one prime.
In May 2014 when i purchased the K3 the DA*16-50mm f2.8 was my main wide angle walk around zoom. This is a very good lens, and is also water/dust sealed. The downside is the lens is relatively heavy and bulky.
In an effort to lose some of the weight and bulk associated with the DA*16-50 in August 2014 I purchased the Pentax water resistant kit lens the DA 18-55mm WR. This lens travelled with me for nearly a year, but I found I didn't use it so much - more using primes for better image quality.
The DA*16-50 was also neglected during this period.
August 2015 saw a very good quality (like new) Pentax HD DA 20-40mm f2.8-4 WR lens came up second hand at a very reasonable price. I purchased this DA 20-40mm. The lens has water resistance, very good image quality and light weight. This lens has become my wide angle walk around lens, that stays on the K3 as the default lens in the bag.
Subsequent to the purchase of the DA 20-40mm I have sold both the DA*16-50 and DA 18-55 WR lenses.
If I need wider that the 20mm provided by the zoom I have the DA 15mm f4 Limited prime in my bag, which is a very good little lens.
So far the DA 20-40mm Limited has proved to be a very good lens, and I have been quite happy with the images I am getting from it.