The incorrect verb is contains. The verb that agrees with the subject and sentence should be contain because a rule of subject verb agreement states that <em>subjects</em><em> </em><em>joined</em><em> </em><em>by</em><em> </em><em>"</em><em>and</em><em>"</em><em> </em><em>takes</em><em> </em><em>a</em><em> </em><em>plural</em><em> </em><em>verb</em><em>,</em><em> </em><em>and</em><em> </em><em>a</em><em> </em><em>plural</em><em> </em><em>verb</em><em> </em><em>has</em><em> </em><em>no</em><em> </em><em>"</em><em>s.</em><em>"</em>
In this sentence, the subjects are the peanut butter and microwaveable popcorn. It is joined by "and" and as the rule states subjects joined by "and" take a plural verb which has no "s"
