The rules change on what you can bring on regularly so be aware.
We have in the past brought on Gatorade, and some breakfast / granola bars, and crackers, pringles or other chips in those cans so they don't get crushed. I have brought on juice boxes or capri suns. We normally order bottled water and soda for the room thru the cruise line. When heading out on excursions, I like to have some snacks and drinks with us this cuts down on buying snacks, if you like you can get those flavoring packets to add to your bottled water.