What is the pH of saltine crackers?

It doesn't have one.....

is related to the concentration of ##H_3O^+## ions when a substance dissolves in water. The concept of pH cannot be used when considering substances that do not dissolve in water to form ##H_3O^+## ions. For example, sugar.

Saltine crackers are essentially of flour, yeast and baking soda. Flour and yeast are not soluble in water, so pH cannot apply. Baking soda is water soluble to an extent, and is a weak base. But in baking the cracker the backing soda will have reacted with any acidic components to create the usual levening effect, so in the finished cracker there should be nothing water soluble, acidic nor basic present.