Last weekend I went to Hudson, NY, to enjoy some really good food. I took my good old Condor 3-day assault pack and followed this advice on how to pack for a weekend trip. The video says that I should only pack whatever is strictly necessary but, just in case, I added three more underpants (because there's never enough underpants.)
Basically, you should lay down all the things you want to take first, thinking about each day and occasion of the trip. Be critical with your own choices and get rid of anything that is not fundamental -- stick to the essentials.
Rolling your t-shirts, jeans, and underwear -- anything that doesn't wrinkle -- is always the thing to do.
Another good tip is to create "daily outfits" by rolling socks and underwear inside a t-shirt. If you are using long socks, fold the ends around the rolled t-shirt to make it extra compact. You can also roll your socks and place them into your shoes. You can line your belts along the sides of the back or roll them inside the collar of your shirt -- that will also help it from getting smushed. Leave the shirts and other items that can wrinkle for last.