1. Condoms

For the sexually active, keeping a supply of condoms on hand is a good way to avoid embarrassing situations, like being forced to run out to the store in the heat of the moment. Another advantage to stocking up is saving money. Condoms can be expensive, but the more condoms you buy, the cheaper they usually are. For example, a recent price comparison revealed that a pack of three Trojan-Enz condoms sells at retail for about $5.99, or about $1.99 per condom [source: Walgreens.com]. A 36-pack of the same brand can be found on Amazon.com for only $11.95 or about 33 cents per condom [source: Amazon.com]. Costco sells a 40-pack for only $9.99 [source: Costco.com]. Condoms generally don't expire until four or five years after they are manufactured, so they likely won't go to waste [source: Trojan Condoms].
Read on for more information and tips on how to improve your shopping habits.

2. Diapers

baby diaper
Thinkstockphotos.com/Charity Myers
Diapers are a huge expense for parents of any child not quite potty-trained so buying them in bulk can be a big money saver.
Any parent knows that diapers for a newborn baby can be a huge expense. Child rearing information site babycenter.com estimates that the average baby's diapers cost about $1,100 in a single year [source: Baby Center]. At a warehouse store, or by waiting until your local grocery store has a sale before stocking up, you can save in the neighborhood of 25 to 35 percent of those costs, resulting in more than $350 in annual savings [source: Switchyard MediaWallet Pop]. But don't let your purchases outpace your baby's growth and don't buy too many bulk packages all at once. Wait until your baby has just graduated to a new size to stock up.