Prepare all of the clothes you need to pack. Especially when hurried, you may want to toss half the clothes you own into a bag and cross your fingers, but setting out everything you plan to pack before you begin is key in maximizing your space and keeping things wrinkle-free. Allow wool pants to "rest" 24 hours before packing them -- don't wear them -- so that the fibers can return to their natural weave. Hang them on a hanger with a thick cross bar to prevent creasing.
If you have a garment bag and you can carry it on, your pants will be thanking you. Keeping pants hung up is the surest way to keep them wrinkle-free, so leave them draped over that hanger, and layer on shirts and a jacket (this will keep the clothes from being crushed). Cover the entire hanger with a dry cleaning bag, so that the clothes on separate hangers will slide around rather than wrinkling.
If you're working with a suitcase, however, packing pants becomes trickier. Once the indentations caused by the handle in the bottom of the bag have been filled with clothes that can be wrinkled (like pajamas and workout clothes), layer in your first pair of pants. Place the waistband at one end of the bag, and allow the legs to drape over the opposite end. Add the next pair of pants, but reverse the placement, starting at the other end of the bag. Continue adding pants, alternating directions. Add the rest of your clothes to the bag, and then fold the ends of the pants over the top. This will prevent the weight of all of your clothes from pressing a crease into your pants.
Unpack at your destination. As soon as you arrive, hang all of your clothes up immediately. If your slacks have any wrinkles, you can hang them in the bathroom while you shower, allowing the steam to release the wrinkles. If necessary, press the pants according to the care instructions, but avoid excess ironing whenever possible.