If you wish to serialize multiple objects into one file, just simply combine them all into one object.
For example, you have a lot of objects need to serialize like these:
Teacher t = new Teacher();
Student[] students = new Student[] { ... };
Tool blackboard = new Tool();
...
And all of these objects should be serializable.
You can create a container to contain those object, and serialize it.
[Serializable]
class School
{
Teacher t;
Student[] students;
Tool blackboard;
}
Now, you just need to serialize the school object into one binary file.