I like to have a clean t-shirt, clean underwear, and a clean pair of socks for each day....so 5 each of those. Depending on how warm/cold/wet it may be I will adjust my top layer to accomidate that. Jeans or shorts?......I like to use lightweight pants w/zip off legs that cover both, when I can. Do I need a jacket/sweater/sweatshirt/fleece? A nice fleece can take the place of a jacket liner or some of the newer jackets have liners thst zip out and become lightweight jackets. Can also be folded and used as a pillow. I'll bring sandals/flip flops many times because they take up less room than shoes and can also be worn into showers at campgrounds. Rolling vs folding for packing...rolling takes up less room. I try to remember to bring a new kitchen garbage bag to put my dirty clothes in and keep them seperate from clean clothes. Only things in addition are a shaving/bathing kit, a hat, and something to read. I'm sure others have more ideas, but this is the basic setup for me.
I can get all that into my pair of givi E22 hard bags, which are 22 liters each, and have space left over to carry a plug kit and small inflator, along with a rain jacket and extra pair of gloves.