Originally Posted by
ROCAT
... If you have big bags I would suggest forwarding them ahead as the trains have very limited storage space, really just and overhead rack.
Not bad advice but to be clear, the airport express trains (Narita Express) have plentiful racks at the end of each car for luggage in addition to rather skimpy over-seat racks for small bags.
The shinkansen has limited luggage space but you can usually find room for bags at the back of each car, behind the last row of seats. It is shared space but most folks are pretty good about making it work for everyone.