Lately, I have been using my 35mm F2 AFD quite a bit on my D300. I like my 12-24 F4AFS but the petal lens shade is too darn big. I am thinking of filing it down on the petals so I have some protection for the front element. I could carry two lenses most of the time; 12-24 and 85mm. Or 12-24 and 50mm. I am curious about the new 50mm F1.8.
A buddy of mine has just a D40 and an 18-135 lens and takes the most incredible vacation photos whenever he and his wife go anywhere. 18mm is generally wide enough, and 135mm on a crop is plenty long too. That lens is really sharp at the long end and also has nice bokeh, so it also doubles as a pretty darned good portrait lens too. Super light and easy to take around anywhere. My dad has the same exact setup only a D60, and the only thing he's missing compared to my buddy is knowledge on how to drive the camera, and maybe an eye for shots. On an Alaskan cruise last year he still managed to take a ton of great photos just in full auto mode.
I like having a nice selection of gear to choose from, but typically stick with just one lens at a time these days whenever I go out also, whatever I think would be most useful. Maybe one secondary lens as long as it's not too heavy. I've also greatly trimmed down what I actually own, too. Back when I had a full Nikon system with multiple bodies and 15+ lenses both manual and autofocus, it seriously took way too much time just to decide what to even bring, and I hated that. Owning a fewer number of lenses where no range or purpose is really duplicated makes the choice quite easy on what to bring.
Before we had zooms we had single focal length lenses. The 50mm lens was very popular then and usually the lens came with the camera. I remember many years ago spending the whole day with only one lens!
Having only one lens could be limiting but if the photographer knows how to take advantage of the lens the results are usually excellent. One lens only will show the photographer discipline. By the same token, the photographer will have to be selective because one lens alone is not good for all types of photography.
Do you want to learn more discipline?, use a hand held exposure meter. Now you not only have to think about your subject but also about your exposure.
At the end you will be a better photographer.
I have owned a wide range of lens' in the past ten years or so that I have owned an SLR, but now I am down to a 35/50/85, and the 35 is planted on my D700 about 99% of the time.
It's so much simpler for me, it works. I do miss some shots admittedly, but I think having just the one lens has focused my mind on the process of taking photographs as opposed to thinking if I have the right lens for the shot.
Last Friday my friend and I went to the site of the annual Tulip Festival in Albany, NY. (The festival itself was over the weekend; we wanted to avoid the crowds and the weather on Friday was great.) She took a D70 with a 50mm 1.4 lens. I took a D300 with three lenses, the Nikkor 60 mm macro, Sigma 10-20, and Nikkor 18-200. (The 18-200 never came out of the bag.)
The photos showed it's not the body or other equipment, it's the eye. My friend has a wonderful eye and got some exceptionally beautiful photos. I think I also got some very nice shots, some taking advantage of the particular strengths of a macro, some taking advantage of the very wide angle effects the 10-20 could give me. Also I tried shooting toward the sun, showing the wonderful colors and translucency of the flower petals. But her compositions were often superior to mine.
Back in the film days I'd shoot all day with a 50mm. It's still not only a wonderful exercise, but it's all that one needs for a great deal of excellent photography.