I think S Popovski nailed it right, it's really a question of preference. Whenever I'm anywhere, I almost always find a good reason to shoot at 300mm. In fact, I'm looking at my Lightroom library, and out of about 8700 pictures taken with my T2i, 3200 were taken with my 75-300 and then 70-300 lens. 3111 were taken with my 50mm, and finally 2223 with my 18-55. That's for all-time.
Since I bought my Tamron 70-300, this month I shot 1300 shots with that range, 32 with my 50mm f/1.8, and 154 with my 18-55.
So for me, if I were to take one single lens, it would be my Tamron 70-300. If I were to take a 2nd lens, it would be my 50mm f/1.8 for interior shots and night shots. If I were bringing my entire camera bag, with Zoom H4n, SM58 mic, tripod, etc, THEN I would bring my 18-55 along.
But that's just me, I'm really not a wide-angle user. Quite frankly if I had a 800mm lens, I'd probably take over 50% of my photos with it.
Some other people would be 100% happy shooting with a 30mm prime. Some swear by their 11-16mm, it all depends what kind of shots inspire you.
Cameras: Canon EOS 6D, Canon EOS Rebel T3i, Canon EOS Rebel T2i, Canon S90
Lenses: Tamron: SP 24-70mm F/2.8 Di VC USD, SP 70-300mm F/4-5.6 Di VC USD, Rokinon: 8mm Fisheye cine, Canon: EF-S 18-55mm f/3.5-5.6 IS Lens, 75-300mm f/4.0-5.6 III, and EF 50mm f/1.8 II
Retired camera: Fujifilm Finepix s700