Consumables, are you kidding? You attack a ship, take serious damage to your own, possibly lose a man or two when you storm the ship and all you care about is food and water? I doubt there would be a ton or so of said supplies, versus 50 tons of cargo which probably isn't food but needed somewhere, with somebody willing to buy, no questions asked, especially with a discount for no questions and for which sale you could buy a hell of a lot more and better supplies. If YTU is so lacking of natural resources that a ship's food supplies are a major prize, nobody would have ships since they cost so much and you wouldn't have a surplus to build them.
In real life, most, if not many pirates started out as privaters or naval vessels of one side or another and either lost the war or became a pain in the ass to their own side like Sir Francis Drake who was executed by his own side to placate the Spanish.
Since most merchant vessels were not heavily armed, compared to the pirate vessels, if they couldn't outsail the pirates, they surrendered and were looted, after all that is what insurance was for. The pirates might take some personal pretties, ask for volunteers for their ship and the like, then they let it sail on, mainly because they had nowhere to sell the ship, besides, it could be raided again on it's next voyage.