As mentioned by some above, it's all about the quality of the material. Buy wrinkle free clothes that are actually wrinkle free. (I find many of them are no different than cheap clothes.)
I roll my pants around a bundle of socks/underwear/tshirts/etc. That seems to work well - if there aren't any folds or creases, you won't get wrinkles.
I use a suit-er for my shirts. It works, but it took some practice since the carry-on sized suit-er isn't wide enough for my shirts to lay completely flat. I find that if I fold the sides neatly and then fold the sleeves straight down that it works pretty well.
If I do have to iron it the shirt later, it's only along that one crease.
Put the suit-er on top, the last thing you fit in your suitcase. If you put it in the bottom, the weight of the other items (and their shifting when you pick up the bag) causes problems.