Consisting typically of two slices of bread, the sandwich is usually prepared by smearing one slice with peanut butter, which conveniently sticks to the bread. The other is smeared with any of several flavors of jelly (often grape-flavored), jam, marmalade, or preserves. Of great advantage is that the peanut butter will not slide or drip off from the bread when it is put together with the jelly slice, allowing even a child to master its preparation.
Another advantage, compared to, say, a ham and cheese with mayonnaise, is that it will stay fresh for a longer time. A schoolchild who brings the sandwich to school in an unrefrigerated lunchbox could safely eat it as an after-school snack. The United States Department of Defense is researching ways of preserving a PBJ for up to 3 years for its combat troops in the field.