Every trip I've taken, I've paid attention to what I didn't use, and, over time, have pretty much gotten to the point where everything I need fits inside my RT, rather than in a bag on the back seat. I do, however, have to wash some clothes every two or three days.
In the last years of my working life, I was an emergency planner, always thinking about what could go wrong and how to prevent it, and that is a hard mindset to break. As a result, when there is a bag on my back seat, I am always worried about it still being there when I come out of a gas station rest room or a place where I stopped for lunch. I no longer have that worry by packing light.
Four sets of underwear and socks, two or three shirts, two pair of jeans and two pair of shorts if the weather warrants, a quart of oil, tools, raingear, a tire repair kit, an extra pair of shoes, and a small kit bag with toothpaste, toothbrush, etc . . . and a bottle of acetaminophen, camera gear, computer tablet, and associated chargers, and bottles of water, stuffed in where they will fit, and I'm pretty much good to go.
Riding jacket and pants get a steel cable run through the arms and legs and locked to the Spyder, along with my helmet, for lunch breaks.