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Exposed color film.
Color film negatives (I don't care how many layers - still unsafe!)
Cheap "solar screen" mylar filters - they may have a pinhole or scratched coating!
Sunglasses. Even two pair of "crossed polaroids" will do nothing to protect your sensitive sight.
Binoculars or telescope without the proper filters. Of course not! They may be safe during TOTALITY, but ONLY THEN. NEVER point them toward a partial solar eclipse!
Squinting won't do, either. Neither will peering through your fingers.
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Welder's goggles of density 14 or greater. Inexpensive, works well.
Special "eclipse glasses", sold by REPUTABLE companies and rated at optical density 5.0 or greater! Check them carefully for pinholes/scratches!!!
A good quality solar filter (at least optical density 5.0 or greater). Check it for pinholes or scratches by observing the filament of a brightly-lit lightbulb first. I still recommend you use these very sparingly, though.
You can expose TRUE black-and-white film (like Kodak Tech Pan) to bright sun, and use the developed negatives in 2 layers for safe viewing of the sun. But unless you're a professional photographer, you probably don't have easy access to this method. Use another one.
Safest of all methods is an indirect one: The pinhole projector. Various types exist, but basically you need 2 pieces of cardboard. Use a very small needle to punch a TINY hole in one piece. Hold that piece in front of the other cardboard, while FACING AWAY from the sun, and move it until the sun's light passes through the pinhole and onto the other cardboard. A small inverted image of the sun (eclipse bite and all) will be projected on the 2nd piece of cardboard. NEVER use the pinhole to directly look at the sun!
WRONG. The sun emits energy over the entire electromagnetic spectrum, from radio waves to gamma rays. You might be comfortable looking at the sun through that insufficient filter, but your eyes are being bombarded with ultraviolet and infrared rays you don't see, and may not be filtering. These both will do irreparable damage. It may not be apparent immediately, but the damage is there.