If you're near the water, it can still get cold in the PNW, San Francisco, etc. That favors cold weather clothing or a good sleeping bag at the least. Most people won't need truly heavy jackets, but a few undershirts and a sweatshirt or two wouldn't hurt.
And when it gets hot, you can get soaked in sweat in just a few minutes, especially if there is no breeze. You're going to be a pretty greasy and smelly person if you aren't extremely scrupulous about hygiene and don't wash your clothes regularly and thoroughly, so summer can be a very demanding season when it comes to how many clothes you go through. Where I live, it can be around or over 100 degrees for a solid month, and very hot for a few more. At that temp, you only have a few minutes outdoors -- in the sun, maybe less -- before you and your clothes start to get sweaty.
I'd suggest that you'd be lucky if one t-shirt per day is enough, especially if you want to be anywhere in public and if you don't want to sit on your seats/lie on your bed in moist and/or smelly clothing that will then start to make your room smell bad. One pair of underwear will probably be fine if nobody but you is messing around in there, and wearing socks more than a day is highly recommended against. In fact, if you're not hiking, I'd suggest wearing sandals most of the time.
