Itoya is Disneyland for people who love office supplies. I have never found such a store in the US. Itoya is similar to Staples in the same way a Tesla is similar to a garbage truck.
Itoya is amazing, it's like a wonderland of stationery!
I also highly recommend kakimori, which builds custom notebooks that you can select all the parts for (binding, paper, cover, etc.). Really memorable experience, and it's in a quieter residential part of the city (but still fairly convenient/central) that feels very different from the usual tourist spots.
Tragically, due largely to Covid, Muji has only one store left in the US, in Manhattan.
I'm hoping they can bring them back, though, there's nothing to compare to. In the meantime, online shipping works fine for what they happen to offer on the website, and that stock has increased recently, which is encouraging.
I can recommend their luggage in particular, there's just nothing quite like it.
I still see several Manhattan and non-Manhattan stores on their store list, but it does look like they're not in the Bay Area anymore, which is a bummer: https://www.muji.us/pages/store-information
Kinokuniya[0] has plenty of locations in the US if you're around a major city. The one nearest to me is a small shop within an asian grocery store, but the selection seemed pretty good for how small the store was.