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Thanks! Actually this particular set (Retro Urban) was used for a whole bunch of atmospheric horror games this jam :D It fits it quite nicely, very different/unique, for a Kenney asset.
As to the items, iirc you need to find 7, but there are 11 items total, so 4 of them are "research notes" (duds). Sometimes you'll get all 7 in a row, sometimes you'll get some notes inbetween. It's possible of course to get unlucky and be forced to actually find all 11 items, but most of the time you don't need to.

That said, two of the items are out in the forest, slightly hidden (exploration!), and one is rather unfortunately placed so that it's blocked by a building most of the time (my bad).

I had a thought that'd one of the items could be a compass-type thing that leads you to the next nearest item, one item could be a "warning beacon" type thing that warns you of the movement of the UFO, and one could be a straight-up map that just shows you the whole area (like a minimap). I also thought some of the items could be utility items, e.g. you need a crowbar to open a locked gate, or a security keycard to unlock a chest etc. That'd make the whole thing a little more 'metroidvainia-like', only giving you access to certain places once you have certain other items. But a) I didn't have time and b) it might have made it very annoying indeed to play. Ah well!