Your Canon EOS 300 has the ability to take multiple exposure photographs (up to 9 images imposed on one frame of film). You can also put a cheap UV filter on the front of the lens and smear it with something like Vaseline to get a soft focus, blurred effect or cut a shape out of dark card (e.g. a star, heart, diamond, etc) to change the shape of the out of focus areas of your image. There are 'specialty' filters to create split images or colour your image with rainbows (assuming you're using colour film) or turn bright lights into stars.
Since you spoke of not wanting to put your camera in the freezer or other potentially camera-damaging things suggested in the PhotoJoJo article you linked to, you can simply do those things to the film itself - I'd suggest AFTER you've taken your photos. People have put their film through the dishwasher, etc. in an attempt to get weird aberrations. You can also scratch up your negatives AFTER they've been developed, although if you're wanting precise "damage" you're probably better off using a camera that will result in a larger negative. From the effects you wrote about, I can see a Holga in your future - easy to modify, cheap enough to trash, medium format negatives
I'm sure there are a million other things, but there's a little list to start with. I hope it helps give you some ideas.