Use a Parent/Child Lists and automatically tie them together and create them within one form.
|Use Case||The premise of this is not for everything, but useful when you want to track Parent/Child Items. What this will allow you to do is create one form for entering the Parent information and the child items, then track those items in two separate list for reporting and other options.|
Nintex Workflow 2013
Nintex Forms 2013
|View the post here for a more detailed look at this solution Create Parent/Child items using this Nintex forms/workflow with this trick|