Bear has a great implementation of file attachments to notes, you can clip pretty much anything you wish. The app will then show file links inline, allowing for other notes and attachments to be placed as desired. Thanks to the developers love of URL schemes you can then link to the note from Things. You can do all this manually but you came here for the Workflow!
This can be run from the today widget, provides the file picker, and once you’ve decided on your attachment it gets to work. The file name will be used for a note in Bear, and of course an item in Things with a link back to the note.
Despite the need for a work around it actually allows you to clip a few attachments and also make notes alongside for a pretty great experience. I have my fingers crossed for Cultured Code to add in attachments, but they seem adverse to adopting the feature.
Check out some of my other Workflows I have shared over time, these are steadily increasing as I find and make more. If you need any help or want to try and achieve something with Workflow head over to the subreddit and ask away.