you can use the luggage forwarding service; cheap, but is next day, rather than same-day delivery. Depending on your luggage configuration, that might be easier than dealing with it in the train stations.

Another option might be to bring collapsible duffel bags so that you don't need to deal with bulky empty suitcases near the beginning of the trip.

Yes, a collapsible duffel bag in the bottom of one's main suitcase will do the job nicely, and Japan's luggage forwarding services are a great deal for travelers and residents alike.

Send your main bag to your next hotel and put your overnight necessities in a day pack or carry-on.

Donki has a pre-arrival ordering site for tax free purchases now
http://www.donki.com/en/tax_free/

I think they used to offer to luggage forward your purchases from the shop to the airport for pickup. Not sure if they still offer this and I'd prefer to take my purchases back to the room as a wheeled bag is easier to get to check-in than a box. However, this might be a good way to get a (low cost or free) box to check-in if you have insufficient luggage space vs buying another bag.

Actually, for that matter, I'd love to know of a quick & reliable source of < $100 sturdy enough wheeled check-in. Even donki's bags were > $100.

Thanks, we will pack light depending on weather. Appreciate all the feedback.