Fist tip: Instead of plain white carrier bags go for colored plastic bags and trash bags that are see-through. Work out a code for the bags - red is dirty undies, blue is clean undies, etc. Use bags where one look at the bag tells you what is inside without opening the bag, taking everything out, looking at every item and packing it up again and thus making a lot of noise. See-through works best.
Second tip: Pack all plastic the night before!!!!!
Have one (cotton) bag where your soap, towel and clean clothes for next day go into. When you get up you pick up this bag and go to the shower, change your clothes and then come back. Then all you have to do is put your soap and pj on top of your backpack and attach the cotton bag and the towel outside the backpack to dry. And bam, you are ready to go. No rustling around with plastic at all.