I layer my swimsuit, undergarments and my pajamas in a zip lock Baggie, and I half zip it, and then start from the bottom and roll it up, expelling all the air, and then unroll it, so it's flat and very thin. Then I sort of use that as my middle for my bundle style of packing. Or, for cold weather packing, I have used jeans as the middle of my bundle. I roll them starting at the waist and head to the bottom. I find layering the clothing and wrapping it in a bundle maximizes space and ends up with less wrinkles.
As for the zip locks, I put in my undergarments because I am one of those people that invariably gets pulled out and has her bag searched and I cannot stand people rifling through my stuff, and touching my clothes. Grrrr. It also saves space. On the return trip home, I put all my dirty clothes into the zip lock baggies and squeeze all the air out. This way, I have room for any souvenirs.
I am a pretty light packer and I only take a carry on for an 8 night trip.