Depending on the type of newsletter you run, and whether you’re hoping to attract a free subscriber or a paying subscriber, there are a bunch of possibilities that might work for you:
Printable, PDF checklist
Maybe your newsletter is about getting kids to explore great outdoors, and you offer subscribers a list of essential items to bring on a family camping trip.
Maybe your newsletter is about foraging for wild food, and you offer a list of edible plants that can be found in your local area.
Or maybe, as in the example below, your newsletter is about wedding inspiration and you provide a checklist to help couples plan.
All of these provide immediate value for the reader who only needs to open a PDF or document to experience the kind of content you provide.