Bulk purchases make a lot of sense in some situations, but it's easy to assume that buying in bulk is always cheaper. It's not. Do some comparison shopping, calculating the $ per ounce. If something is on sale, it will usually be cheaper than bulk, as bulk rarely goes on sale.
However, my favorite snack of all time, Fiber One bars, are a great deal at Sam's Club, at about $7.50 for 20 bars. This is much cheaper than the normal grocery stores, even when there is a sale.