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When you have old underwear or bras don't toss them out. Wash them and put them in your suitcase, they will be there when you pack. When traveling, wear them and throw them away. That way you got one more wear out of them and won't be packing dirty clothes home. This makes more room for souvenirs
I was talking with a lady at the airport once and she said she and her husband always go the a thrift shop and buy underwear, t-shirts,shorts,nightclothes and socks to take on trips..then leave them or throw them away. Saves space for souveniers on the return trip.
Carry two pillow cases with you when you travel. Use the first to put your dirty clothes in (assuming you don't have access to a Laundromat) and place the second pillow case (if you're in a hurry) between your dirty clothes from the night before and your clean clothes.
I learned this the hard way. Years ago we had a camper and the first week-end we went camping I put our dirty clothes in a garbage bag. At the end of the week-end all garbage was dropped off at a designated site as you existed the campground. I'm sure you can guess what happened--the bag containing the clothes went will all the other garbage bags and gone were our clothes, which I didn't realize until we were home unpacking.