One of the handiest things I've done for years is to carry a calculator in my purse at all times.  It's great for keeping a running total of items I'm purchasing when paying with cash (or whatever method of payment you choose).  It's also helpful at places like Sam's where one price tag might state the price per ounce and a similar item might state the price per unit - a calculator on hand can easily help you determine  which is the better deal per ounce.

Visit Mary to participate or view more Tightwad Tuesday entries.