Collection of *interesting* encounters by terrain (including urban, sewer, ruins, crypt) and by level that I can toss in when I need a fight that I haven't prepped. By interesting, I don't mean "I picked some monsters and plopped them down on appropriate terrain", rather interesting terrain and hazards, outside factors, 3rd parties, other win conditions that predate Pokemon: "Gotta slaughter them all". Even interesting mixes of foes with quick tactics, things you wouldn't see. Preferable all of it done efficiently - encounters good for several terrain types with some reskinning or minor changes, notes for adjusting the difficulty, etc.
I'd want them packaged by Tier or something similar, so I can pick up a product for my campaign, picking up more as needed.