The United States Postal Service (USPS) employs a large number of employees to deliver mail around the country at the rate that it does. There are certain jobs within the USPS that are referred to as "casual" jobs. These are essentially temporary postal service jobs, and they only last for 89 days, just short of the three month testing period that most jobs have for new employees. Getting a casual job with the USPS takes some effort, but the standards are easy to meet.
Locate casual position openings with the US Postal Service. You can watch for job postings in local branches, or you can go to USPS.com and search for jobs on the website. This will require making a profile on the site, but you can also apply for jobs that you find through the website using this same profile.
Review the requirements for the position. Casual jobs with the USPS require that you be 18 years old or a high school graduate, that you be registered with the selective service (if male), that you can list your employment history for the past 7 years, and that you live within 50 miles of the center where you will be employed.
Apply for the position. The position description will list how to apply. You can put together a physical application with your resume to turn in at center that's hiring, or you can apply online. Once you've completely filled out your online profile as USPS.com, it will have all of the necessary information so that you can apply online.
Pass your interview, your drug test, and your training. Once you make it through all of these steps you are an official casual employee of the USPS, and you will be employed until the end of your 89 day period, barring anything that would get you fired.