For the Core City faction buildings, I just told each of them I was looking for a job without actually taking the job. They all let me visit the lower floor as I liked: I still had to sneak for the JKK 2nd floor, but for the Praetorian back office, all I needed was a flashbang. I still managed to do the Coretech questline after that
I would have never got the Long Rubber Glove if I hadn't spoiled myself. I never join the cans, and I would probably always reload if I triggered the alarm during the drone mission lol
For some reason, my first two or three Hard playthroughs, I could get the two-headed mutant reliably, but the last 3 playthroughs, I haven't had a peep of him. Maybe we have to pay Kareem for the rumor now? Oh well, at least my Super Steel luck has always been solid.
I think the other "easy to miss" oddities are any entities in containers that aren't highlighted by TAB. There's one by Hardcore City Bar, and a few in Foundry. I haven't found any other I think, but I'd like to think there's more out there.