I believe that Costco (NASDAQ: COST), Royal Caribbean (NYSE: RCL), and Sirius XM Holdings (NASDAQ: SIRI) are buy-and-hold investments, and that won't change the next time there's a market sell-off. CostcoThere's a good time to buy Costco stock, and then there's a great time. Royal Caribbean is cruising with industry-leading margins and growth. There are some choppy waters right now, but to an opportunistic investor, Royal Caribbean is tempting at just 3% higher over the past year. Royal Caribbean slightly lowered its full-year revenue growth forecast from 10% to 9%, but it did boost its adjusted earnings outlook.