What I expected was updating the old (and really excellent) supplement "Aurora's Whole Realms Catalogue" into 5e. Which would be fine. That's actually something I was considering doing myself. Instead, we get a new catalogue with items all designed for summer (think like summer hats, zinc oxide to prevent sunburns, and other summery things).

That's right, all fluff, very little in terms of rules. The rules that are present all make sense and are so situational, they could never really break game balance. If I had a critism about the supplement, it's only that the form factor of the page (which matches the original) is a little cramped and all the illustrations have a white background instead of being translucent (which would make it look like the art was drawn onto the page texture). These are tiny little problems and do not detract enough to warrant removing a star.