Slide projectors can be made quite simply. They're little more than a bright light bulb, a fan to cool the bulb, something to hold the slide, and a couple lenses. One is a condensor lens that goes between the bulb and the slide, the other is the usual lens to focus the image. Oh and I forgot about the hot mirror which passes visible light but blocks infrared.
Hmm, come to think of it, with the advances in light bulb technology and LEDs, the cooling fan and hot mirror may become unnecessary altogether, which reduces the complexity to a light source, a condensor lens, a slide stage, and a focusing lens. I've even seen instructables on how to build a simple slide projector. Projectors I'm not worried about. I'd be more concerned about cameras, film, and chemistry availability.
The Slide Curmudgeon, aka ME Super