Given that you're top-roping, very little needs to be on your harness when you're actually on the route. In fact, one of they joys of top-roping is the freedom from all this clutter! Everything else can be stashed in your pack - I normally clip it all to a short sling, so that I can quickly grab it and find what I need at any time.
For seconding a route, the requirement is similarly low, except it's a good idea to carry a nut key somewhere out of the way (I clip mine to the back).
On lead, you need just about everything (though you might be selective - e.g. leave behind the micronuts if you obviously won't use them, or take only even-numbered sizes to save weight), and then the knack is to have a system that you know by feel (e.g. I carry nuts on my right gear-loop, ordered from smallest to largest, and extenders on the left gear-loop; nut key and belay/abseil device round the back, and slings over the shoulder).