Many successful digital products edge over competition because of their ‘extra’ add-ons. For example, my shop include a template of commonly used symbols and graphics so that customers can copy/paste to their templates. I only have to make it once and I can include it in every template I sell:
Here are some other examples of successful digital product shops doing that:
Some resume template include guides that help their target customers land a job easier. CoResume includes this resume writing guide for free with any purchase of their templates.
Many digital planners include a large library of digital stickers and planner covers. This bestselling listing from AmethystGarnet is no exception.
This shop includes a free editable Airbnb welcome sign (complementary product) to their Airbnb welcome book template.
You can also consider making a free tutorial/use guide for your customers if your product is more complicated to use. This seller includes a Youtuber tutorial for free for customers who buy their Notion templates.