As an adventure writer, I like to think that the story comes first, and is the most vital thing I'm providing. Sure, there are monsters, but you can go get those stats in a monster book (whether a Monster Manual, a Bestiary, or an Alien Archive). The same with traps; something in the core rulebook is something you can look up yourself. Maps are often really important to tell the story, but you can draw those out yourself, or print the ones I include in the adventure. You've got all the tokens, figures, and rules you need already, so I'm not providing those; I'm only providing the story.

This narrow focus on the adventure does a disservice, I'm learning, to what people want and how they play. There are lots of extras that make a game more useful, and providing these has some real value. The extra "bells and whistles" are worth thinking about, and often worth including.

Paizo and other large companies monetize these. You can buy flip-mats of their adventure sites, even though the maps are right there in the adventure anyway. You can get pawns of all the specific characters, even ones that you probably have serviceable models/figures/pawns to use (you can get Chief Gnarl Bonebreaker instead of having to use Standard Orc #23). They have card sets featuring rules, monster stats, spell descriptors, and everything else. These aren't flashy products, but they sell well and are considered necessary components at many tables. Wizards of the Coast does the same, although their licensed partners like Gale Force Nine provide these. Companies that produce products via Kickstarter add these types of supplemental materials as stretch goals, but plan from the outset on producing them anyway since they know gamers like them (and thus buy them).

As a small third party publisher, I don't have a lot of resources to give you boxed sets with lots of maps and standees and soundtracks and such. I can't get custom die-cuts for pawns without enormous expense. But I can look at what else makes running my products easier, and include those things.

Owen K.C. Stephens, who is a great friend as well as a business partner, pointed out that I ought to be including all my monster stats in my products. Even stats that appear right in the Bestiary should be included in my products for ease of running them. He's done more products than I have, by orders of magnitude, and he knows what people want to see. So I've been more consistent about doing that.

But there's even more. My good friend Ken Melvoin-Berg like The Duskwalkers Due, and I tapped him for thoughts on how I could make another solo adventure better. He had several simple ideas (like including a picture for Tarklo Dirge; you should be able to visualize the hero you're playing!) and he had a conceptual idea that resonated with everything I've been talking about above. He said he didn't want to consult another book, because it took him out of the play experience at the time. He thought I ought to not only include full monster stats, but explanations of all the conditions the monsters might give, a summary of al the treasure items, and even a quick run-down of relevant rules where appropriate (such as the rules on disabling traps when a trap is present). 

That's a whole different kind of "bells and whistles" that I can apply very easily (often just cut and pasting from the rules and tweaking the language a bit). Adding value for a low effort or cost seems like a smart move. 

In news that probably won't surprise anyone, I've been working on another, longer solo adventure. With Ken's thoughts in mind, I've not only included all the stats for monsters, but also for all of the magic items you can find. I've been more deliberate in explaining unusual situations (like uneven ground or hazards) so you get everything you need to apply them without having to consult another book. I've included relevant rules; for example, when you meet a healer who accompanies you, I reproduced the rules for Treat Poison and Treat Wounds so you know just how the healer can help you without having to refer to the Medicine skill description. I think these extras will make the final product more fun, and I'm looking for even more bells and more whistles to aid play.