My standard practice for Japan is to go over carry-on only, with the A30. I pack a reasonably large Longchamp folding weekend bag. On the way back, this carries my laundry, shoes, brochures, anything heavy etc, and I check this. In my A30, I have anything that's fragile, expensive and precious, and I keep this as my carry-on.
You are definitely right to plan ahead for shopping in Japan!