Since you want to establish one-to-many relationship = one tracking number, one order but more than one package, you need another recordset.
The second recordset called Packages for example, will have a link via Transaction number, which is your order. Then you will have to add and add-on to display new Tab called Packages. There you will be able to record as many as you want per order. And you can add as many fields per package as you want. I would also attach notes - this way you can even take pictures of a package as it is being sent.
Let me know if you feel comfortable writing a module for EPESI: http://www.epesi.org/Category:Developer_Tutorials