You don't need to put your bag out the night before, you can keep it and walk it off the ship.
However, in my experience (which does NOT include transferring to a WDW hotel, so this may totally not apply to your situation) if you do put your bag out the night before you still pick it up in the cruise terminal to bring it through customs & immigration. If that's the case for you, that gives you a chance to stash some things into your larger luggage. At that point, I think you load your luggage on the bus to the WDW resort and they will take care of it from there. Again, could be totally wrong and I don't have personal experience with this or researching this.