My first answer here isn't so much a hack as it is using something that is on the market to achieve what you want.
Have you ever heard of paper shredding scissors? Basically they are a pair of scissors with multiple (~5) blades and you can use these to quickly shred your paper.
This is what I am talking about:
These can be found on Amazon here.
You could also try burning the documents, just get a metal bucket or something non-flammable to put the bits of paper in and then take it outside and set it on fire - if you smoke it would make a nice outside heater during the winter but could be a bit of a hazard so is something to think about.
Another method: Soak them in water. This method may take a while however but you will be able to dispose of large quantities of documents in any one go - adding things like vinegar or salt to the warm water solution would help to speed up the process.
There are also independent paper disposal companies that you could look into if you want to pass the job off onto someone else. Your local area or city might do a document destruction day which you can hop along to and destroy all your documents for free but you would have research into this.
- Shredding scissors
- Water or chemical solution
- Independent companies / destruction day
My personal favourite would be the water one, you could also use bleach which would do more damage and I would personally give it a good mix with a long stick or something to really break up the paper. Even if the paper doesn't tear apart, most of the writing should become illegible so it wouldn't even matter!