However, there is a lot of wisdom in what is being said. On my first tour in the early 80s, I carried a pair of jeans also. However, I was a young 17-year old who could sprint of hills with ease on a fully loaded bike. Plus, I didn't know about nylon pants then. I sure would not bring them now due to bulk and weight. Plus I only wore them like 6 times in 84 days. For me, I really try to get at least 2 uses out of everything if possible, i.e. my riding shorts are typically a khaki baggy style so I can wear around town and not have to carry too many sets of "street" clothes. Again, this what works for me and I would not expect others to agree to my thinking on this. Like others, I use zip-off nylon pants but they double as my swim trunks since it has a nylon mesh liner.
I personally hate to do laundry so carry 3 pair of riding shorts, 1-2 lightweight wool t-shirts (no, they are not hot plus they don't stink if not washed), 2 long-sleeve nylon shirts (I am very susceptible to skin cancer so typically ride in LS shirts), 1 pair of nylon zip off pants, 4 pair of socks, 2 underwear (usually wear twice since only wear a few hours a day), a pair of lightweight sneakers, and depending on the weather, a lightweight riding jacket. I also carry leg warmers to keep my legs warm without another pair of riding pants if the temps might get cool. Some think that is way too much, some think it is not enough. For me, it is about right, but I agree is more than "average". I typically get 4-6 days out of it before a laundromat visit depending on the mileage, weather, and if I can rinse my clothes out.
Another thing to consider is that the TA Route has a wide range of weather conditions. When I rode it in the 80s, I had 105 degrees near the OR/ID border to getting snowed on July 4th in Yellowstone with a high of 34 and lows into the upper 20s. So some cool weather stuff is needed also. However, you can always mail yourself stuff care of general delivery so you don't have to carry warmer clothes the entire way across the country. Temps between the east coast and Pueblo, CO, will be similar. Once you get into the mountains, it does cool off, especially at night and/or cloudy days.
In summary, bring what makes you happy (and can carry). You can always mail it back home and/or buy more on the road. Most of us have done that.
Enjoy the ride, John