I have been eyeing this case logic camera/2 lens sling:
Amazon.com: Caselogic XNSLR-2 SLR Camera Sling/Shoulder Bag (Black): Electronics
It is pretty compact but the photos indicate it should hold my kx, 16-45 and 55-300. Sure its case logic - but I have one of their tripod cases and it is actually very well made. I also like that it is almost messenger style, with a top load that can be used over either shoulder (alot of slings are over the right shoulder, which just isnt comfortable for me...one of those things I guess, maybe because I am left handed...)
If you want some more room, and space for a few extra things besides the camera, I would also recommend a look at the Kata 3n1 series (the 3n1-10 would be perfect for Kx and a couple of lenses, lunch and/or a light jacket).
Amazon.com: Kata KT D-3N1-10 Sling/Backpack (Black): Electronics
I have the 3n1-30 - same bag just wider, it is almost a backpack (the 3n1 series can actually convert to a backpack, and be slung over either shoulder, a unique design in the sling bag department). the 3n1-30 can hold almost everything I can throw at it (that is, most of what is in my sig), great for vacation!