The flash on your camera can cast harsh shadows and bright spots on your subject. You can soften your flash by taping a coffee filter in front of it. Or, you can just hold a filter over the flash if you can't stand the idea of tape touching your camera.
When you're babysitting someone else's kids, you may not have any kid-sized bowls in the cupboard. Coffee filters are just the right size. Fill them with pretzels, chips, cut veggies or popcorn and toss it when they're done.
You can put a filter in the bottom of your flower pots to keep soil from seeping out of the drainage holes when you water your plants. Just make sure that the filter covers the drainage holes. For bigger pots you may need to line the bottom with several filters.
You can make vodka taste better by filtering it through a coffee filter several times. Just use a rubber band to secure a filter to the mouth of a jar or glass and pour it though. Using a water pitcher filter takes less time and produces better quality, though.