[Nyororin]

How big are you talking about? I`m imagining normal sized suitcases?

Stand with them at the end of the aisle, or if you are on a fairly empty one sit in the very front seats and store them in front of you. People take skis, snowboards, and the like on the shinkansen all the time - I doubt you have anything bigger than that. You just have to keep it with you. Trains don`t have somewhere to store the things.