One thing I really like to do is take something meant for one purpose and make it do something else. I recently took a model rocket and encased it in what looks like an RPG (Rocket Propelled Grenade) warhead. I then made a launcher out of PVC pipe, put the electric launch guts inside and presto! I had a rocket launching movie prop. I realize that this may be similar to the orginal intent (it still acts like a rocket, after all), but there is no chance to "stand clear" when the thing is sitting horizontally on your shoulder opposed to veritically on a launch pad. Plus, after lopping off the fins and making it wire-guided, it was a pretty different animal when I was finished.
There are other examples of this. A bucket can make a great child's hat, a clicker pen can be a spring-loaded pistol, and a key ring can make your zipper work again. It's only a matter of looking at things with a more open-ended perspective and determination.
It's easy to feel guilty when you are taking something that works perfectly fine and "ruining" it. Sometimes a little destruction is necessary in the process of creation. The point is that you are taking something mundune and conventional and making it unusual and unexpected. What's wrong with that?