A student laptop contains a lot of important school work and usually personal data such as photos. Although hard drive failure and computer theft are relatively uncommon it is strongly recommended that students use an external hard drive to back up their data. Apple computers have a system called Time Machine that makes backup extremely easy. The bundle deal includes a large backup drive. If you are buying a backup drive outside of the school deal avoid buying one that has firmware based password protection. Recommended specifications for a backup drive are minimum 500GB capacity and USB powered.
As mentioned elsewhere Rule Number 1 in computer care is BACKUP. Your data is the most important part of your computer and should backed up at least once a week.
Backup for an SSD Drive (Macbook Air and Retina Macbook Pro) is absolutely critical. If an SSD drive fails there is little chance of retrieving data.
Link for Time Machine information and setup