stock up 囤貨
     It means to buy a lot of a particular thing, in case you cannot get it later, or because it might be more expensive later.
     eg: When there's a storm coming we always stock up on food and candles.
     Note:
     stock up的意思是特意大量購買某種東西，以備不時之需或者以免將來價格增高。
     例：我們經(jīng)常儲存大量食品和蠟燭以防暴風雨來臨。