I know many people don't like math, so here's a quick explanation of how to figure out unit price:
Take the price of the item and divide it by the size or weight (ie ounces or pounds). For example, for the 5-pound box of Cuties, I did: $3.99/5 lbs = $0.80 per pound.
If you want the unit price per ounce, simply divide by 16: $0.80/16 = $0.05/oz.
Some stores do all the work for you and print the unit price on the shelf tag, usually in ounces. It is useful to memorize that $1/lb = $0.0625/oz. Knowing this, you can simply look at the price per ounce on the tag and estimate how much you are paying per pound. If the shelf tag says an item costs $0.19/oz, you know you are paying about $3/lb.