What to do between getting off the train and setting sail?



First time cruiser.
Trip Seward to Vancouver
HAL Veendam

We are taking the train to Seward, and it gets in around 11:30am but you do not have to be on the ship till 4pm. What should or could we do in the mean time?

Are you able to go "check-in" on the ship and then leave and get some thing to eat or sightsee in Seward, or do they frown on that?

If we can’t leave the ship once on board, can we check our bags at the port and then go eat or something in town?

Or will there be so much to do between getting off the train and time to be on the ship, at 4pm, that we will not have time to do anything in Seward?