The phrase "to stock up" means to purchase or accumulate a large quantity of something, usually with the intention of using it in the future. It can refer to buying groceries, supplies, or other items that you need for your home or business. The term is often used when talking about preparing for an event or emergency situation where having extra inventory on hand could be necessary. For example, a person might say they are "stocking up" on canned foods and bottled water in case of a power outage or natural disaster.