I find that I can never use a whole "bunch" of cilantro before it starts turning black (dark green?). After I buy it, I typically wash it and lay it out to dry for several hours. That definitely extends its lifetime by a few days, but still not long enough. I run into a similar issue with spinach, but less frequently, as I'm usually able to eat it all sooner. I also notice that spinach seems to produce condensations on its own, inside of the plastic bag, which I assume causes it to go bad quicker.

Is it better to keep this stuff in paper bags, or maybe an open container?

Upon arriving home from market, I immediately trim the bottoms off the stems of the herbs with sharp kitchen shears, and then put the bunches upright--unwashed--into old highball glasses filled with enough purified water to reach all stems. I add a drop or two of Willard Water to the water, and that seems to feed and preserve the plant. I then cover each bunch loosely with the grocery produce bag in which I brought it home. This helps to seal in humidity, without smothering the leaves.

When I am ready to prep herbs for use, I wash only as many bunches as I'll need for two-three days. I immerse the herbs in a low food grade hydrogen peroxide/water solution for a few minutes, then rinse the herbs well and spin them almost totally dry in a salad spinner. I then place the herbs in another clean produce bag from the grocery, and place them gently in my crisper drawer, always on top of anything else in there. I find that this process keeps the herb as fresh as just-picked for a few days and keeps them from getting bruised. Herbs are very humidity sensitive--if you wash them or just store them damp in a drawer in the fridge, they will immediately commence rotting.

This is the directions i got from a CSA once to extend the life of leafy greens. first, don't wash it (unless your going to use it of course) right away. wait until it starts to get a little wilted, then give it a bath in some tepid water, shake it out, then put it back in a plastic bag or container on top of or loosely wrapped with a paper towel. the tepid water bath really perks them back up. That's the way to baby them greens

I have found a salad spinner is GREAT for extending the life of all my greens.
Wash them and put in the spinner and spin the heck out of them.Spin,then shake them all around,then spin again,then put into zip lock bags with the zip opened just a little bit.Dont close it all the way.
I have romaine last up to two weeks like this.
Vin

Also,this might sound trivial.
But keep shaking all your stock daily.
If stuff sits too long it pools water and gets mushy.
So go in and shake your bags even if you dont use something that day.
Vin