Adding a feature that would allow you to take a picture of a receipt and upload it to specific transactions to reference would be a nice feature.
That feature already exists.
My Receipt column is at Column J on the Transactions tab.
Below is an excerpt from a Help Desk article (and a link to the whole article) and a link below that on a related topic.
Track business receipts
The Transactions sheet contains a column called “Receipt”. Use this column to pair transaction line items with attachments stored in the could. When URLs are placed inside Sheets cells, they can be clicked for instant access to cloud content— like a detailed record of a purchase.
- Create a folder on your Google Drive for “Receipts”. Each time you make a purchase take a picture of the receipt, or save it to PDF, and then save it to this folder on your Google Drive.
- Paste the URL of the receipt image in your “Receipts” folder into the Receipts column on the Transactions sheet.
Here is a thread on a related issue.