If you're in the bulk-shopping mindset, you might start thinking that bigger is automatically better. But that's not always true. If you check unit prices in the soda aisle, for example, you might discover that it's cheaper to buy a case of cans than a few liter bottles. One word of caution, though: Unit prices aren't always based on the same measurement, so it's easy to get tripped up if you're not comparing apples to apples (or ounces to ounces). There's no shame in whipping out a calculator to make sure -- in fact, we encourage double-checking prices.