Here are some key areas to examine and deal with any employee departs, no less important with a summer hourly worker than a long-time member of your team:
Log-ins: If you issued any workers log-ins or other network access tools, change them before the employee departs.
Passwords: Cancel any passwords and log-ins the employees created themselves.
E-mail: If you issued the employee a company e-mail account -- or any other type of account, terminate it immediately. The same goes for posting privileges on company blogs or social network pages.
Workspace: Look under the employee's keyboard and in other "usual suspect" spots (desk drawers, behind monitors) for reminder notes the employee might have written regarding passwords and other security matters.
Equipment: Audit the departed employee's computer or other equipment for personal software that's still active (if you allow personal software on business machines), being sure to check as well any modifications to browsers and other apps. Look carefully for auto-fills that remain active even after the person who created it has departed.
The goal is is to ensure that when the employee is gone, all access privileges and potential security vulnerabilities are gone as well.