There are lots of bargains at the dollar stores but make sure you check prices by unit value and not container as many of the items are sold cheaper because the producer has changed the size of the container. What you definitely don't want to buy are:
Toothpaste - It has been found to have poisonous substances for some tested and not worth taking the chance.
Electrical Products - Wiring may be substandard. To be safe, don't buy anything with a plug.
Vitamins - The FDA doesn't regulate vitamins and dollar store vitamins may have missing vital ingredients.
Children's Toys and Jewelry - Some may contain lead.