you paid for it. But yes, get on the ship as early as possible and start eating that food you paid for. Having been on about 15-20 cruises, we try to get on as early as possible, start exploring the ship, eating some lunch, take care of your emergency procedures you have to do before the ship leaves.

And pack your swimsuit in your carry on so you can hit the pool that afternoon before the crowds arrive. (if that's your thing)