The best replacement for invoices is receipts.

The best alternatives to invoices are rated as following:
★★★★★  receipts
★★★★  statements
★★★★  bills
★★★  sales receipts
★★  purchase orders
★★  sales receipts quickbooks
★  invoices
★  sales orders
★  copies of invoices
★  bids
  vouchers
  billing statements

Your alternative for invoices is not listed? Suggest!
Speaking about invoices, one probably shouldn't forget about shipping labels.

Other search terms related to invoices and their ratings are:
★★★★★ shipping labels
★★★★ purchase orders
You have in mind a companion for invoices and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of invoices in all years. Click on graph for more.
invoices
receipts
statements