Anything with a core or thick stems: I slice off 1/8" and stand the item in about 1-2" of water.
Brussel sprouts: I again slice off a sliver to reopen the cell structure that may have dried shut, then put them in a container and fill the entire thing with water. I'll check on the firmness each day: in 1-2 days they will be rock hard. Then I drain and put the damp sprouts back in the same covered container.
Kale: here it comes in looses bunches of big leaves. I either fill my sink with cold water or the largest bowl and again, nip off the ends. They will refresh back to feeling crunchy. I drain those, then process about half the bunch by stripping of the thicker stems and then watching a movie, I'll strip off the smaller stems and place the small leaf pieces (now about 2") in a bowl. When I have a bunch of cleaned stemless leaves, I crunch those with my hands after dressing with olive oil, lemon juice and a bit of agave. Now I have a container of ready-to-eat kale that I can either eat as a salad or add to whatever.