During the course of a typical work day, I might use up to 6 different computers, 2 at home and 4 at work. Keeping one set of information constantly updated, and always coordinated between computers is very important. Grades and attendance, for example.
I use a system where I carry a USB memory stick (also called a thumb drive) with all my important data. I always save the newest version to the memory stick when I edit and save a document. Every 3 or four days, when I save to the memory stick, I then copy everything on the stick to the computers I am using. That means I have 6 backups, but the files I use are on the memory stick.
You can buy a memory stick now for very cheap. I bought a 2 gigabyte stick 3 years ago for 20,000 yen. Yesterday I bought a 16 GB stick for 4,000 yen. Most people would never use more than 1 GB. But if you start using audio or video files, the sticks can fill up fast. If that is the case, try a portable hard drive. They now cost less than 10,000 yen, and give you 120-320 GB and more. This is a great way to back up your laptop, or carry it instead of the laptop when you visit friends with computers.
A quick note on terminology in English. Memory is usually a computer chip used by the computer to run software faster. It usually stays in the computer. Storage is used for files and data that you save for using later. So when I am typing something in a word program, I am using the computer’s memory. When I save the document, I am using it’s storage. So the name memory stick should really be storage stick. But it’s not.