I'm not sure what purpose that would serve. All an invoice shows is that you asked to be paid. Since most shoppers and small business owners are on a cash basis, only payments received would count as income for them.
Maybe I am not quite understanding what you want to know.
Based in MD, near DC
Shopping from the Carolinas to New York
Have video cam; will travel
If you are wanting to use them as your records of shops you have done, they would serve that purpose. However, they aren't official as Walesmaven says above they are just you asking to be paid. Therefore, they don't count as an official 1099.
Shopping across Indiana but mostly around Indianapolis.