Wife and I went to Ireland for 12 days and had carry-on only. We knew we would pay for the hotel to do laundry once.
1. Sucks to pay for laundry, but its a one time expense and the trip was long enough it made sense.
2. The underwear and shirts I take can be rinsed in the sink and dry overnight or are material that resist odor (duluth, merino, etc). Fewer pairs needed.
3. Socks are always merino and can realistically get 2 days without odor. Fewer pairs needed.
4. I screwed up on shoes the first time. Pack the running shoes and wear the chukka boots or whichever shoes are biggest.
5. Packing cubes and travel bottles for shampoos, soaps, etc really do help save space.
6. Roll clothes. You may need to iron a bit but for the most part things come out wearable if rolled correctly.
7. (Controversial) I went exclusively with travel style pants (prana). I’m still working on getting a pair of jeans into the mix consistently because they are bulky to pack. When we went to Sydney i managed to do it.
8. Wear jacket, midlayer and I even had a thin vest onto the plane. Those are useful for padding while u sleep or usually fit in the overhead and save space in your bag.
I will edit if I think of more. But we each fit into our own osprey farpoint backpack (it has the main bag and a zipoff small pack). I am an over packer, but when I forced myself to try minimalist once, its kinda fun to take the challenge.
Nerd alert: Before we left I took a pic of everything I was putting in my packs. When we got home I took a pic of all the crap I didn't use and that helps improve the next trip.