Including a resume 
Do not include a resume if the application expressly says not to.  If there are no instructions regarding resumes, only include one if the resume includes relevant information that is not addressed somewhere else in the application.  If you decide to include it, tailor the resume to the law school, highlighting relevant work and extra curricular experiences as well as appropriate skills. 

The addendum
Addendums are used my applicants to clarify weaknesses in the application.  This allows a student to provide additional information to the admissions committee without having to include the information on the personal statement.  Students often use an addendum to explain why their GPA or LSAT score is not an accurate representation of their abilities or aptitude in law school.  If using an addendum, be brief and sincere, focusing on how a similar weakness would not occur again.