I have never had enough clothes to last a week on vacation without doing wash, with the exception of my DH's and my trip (alone, no kids, first 5 night trip ever doing that 8 years ago) to Peter Island. There we wore our swim suits so rinsed out daily, and a basic attire in the evening, so I hung stuff up that I had rinsed out all over the room (housekeeping must have had a chuckle). But that's the only time I've gone without laundry on a vacation ever.
I like clean clothes - a shirt worn even half day is smelly to me. Shorts, yes, I'll wear twice (at home 4 times!).
We used to live on Oahu, and we go back every other year or so, and one trip, I was taking the kids (well, most trips we met there) and DH was coming from a work trip in AZ, so anyway, we were in first class (not all trips were but thank god it was this trip) and we each had a small carry-on). Someone asked about our bags, and I said that's all we had. These were small less than 21" carry on bags. I said we were going for two weeks. They said wow - I'm like, we have a washer/dryer and we were making a Target run the day we got there (me in full on zombie mode after 2 hours sleep but yeah, for toiletries and such - 10 minutes from our timeshare).
The stuff you need for a weekend trip or a two week trip - it isn't that much different, give or take a shirt or dress!