What to pack?

So I'm travelling around Japan for 27 days. I have never been away for this long before and I am trying to travel light. I understand weather wise it can be quite cool so this is what I am planning to pack. Does it sound ok to you? Am I missing anything? How easy is it to wash and dry clothes?
x1 combats
x1 jeans
x2 leggings
x1 waterproof with lining coat
x1 jumper
x1 cardigan
x7 tops
x1 dress
x1 bikini (onsen)
x1 trainers
x1 flip flops (onsen)
x2 bras
x10 socks
x10 pants

Is this too much, too little?
Thank you ^_^

When and where are you travelling?

How much you pack depends on how often you plan on doing laundry. From your list it looks like you are aiming to do laundry about once a week? Personally I'd cut it down a little and just do laundry more often. Coin washers and dryers are pretty easy to find, especially if you are staying at more budget accommodation.

btw, what onsen are you planning on visiting? You won't need flip flops for any of them, and the majority don't allow swimsuits to be worn either.