Make a list of activities that you will be doing. A swimsuit is important if you plan on going to the beach-maybe not as important if you will be staying in B&B's and traveling across country. I packed a light robe once because I really wanted it when my girlfriends and I rented an apartment in Paris-it was an old one with a bleach spot or two but it kept me cozy in the evenings. I tossed it in the trash before flying home.
Throwing out clothes along the way leaves room for the mementos you pick up. Most of us have the mindset to wear our best clothes when traveling, however, look around you-only the tourists are all dressed up. When in Europe you really want to look like a local-it is safer. The Europeans wear clean but understated clothes-no white tennies. They are not as concerned as Americans about everything matching. I take clean, neat clothes, blacks, whites and beige with 1 color accent-but not my newest, in fact I take at least 1 pair of pants that I am going to throw out along the way. I take 1 washcloth for every 5 days I plan to be away and throw them out (leave them in the bathroom) when done with one. I also take my oldest undies-forget what your mother told you about no holes in your undies in case you are hit by a car and are taken to a hospital, I take 5 pairs and wash them at night in the room and then throw them out one by one on the last leg of the trip.
You are going on a trip for the experiences not to be a fashion plate. Wearing comfortable, lived in clothes relieves the stress of loss and gives you room in your suitcase for the "small" trinkets you are gathering.
Last thing-shoes. On my first and second big trip I only took one pair of nice looking and comfortable walking shoes-Clarks. However, on my third trip I added some comfortable walking sandals-it gave my feet a break and allowed the shoes to air out-worth the extra space.