It's actually an interesting thought exercise to come up with a setup that would:
a) allow you every day access to your data in a practical way
b) allow you to get rid of the data, leaving no trace that it was there
Modern software leaves bits of information everywhere. Lock files, history files, logs, cache, etc..
If you re-image your disk to do an emergency destruction, the new image is probably going to be fairly obvious. Huge gaps in all system logs, and an old version of firefox with the last history entry from some time 4 years back? Yeah, this is what was on here 10 minutes ago! If you use that approach, you'd have to keep your "emergency image" in a state where it looks used. And that's not accounting for the fact that re-imaging a drive isn't exactly a quick process.
The other option of course is hidden volumes. But that then strays into the practicality side of it. How do you use something on a regular basis yet leave no trace of it on your system.
Ultimately I think it's a moot point. As has been said, they usually have a pile of evidence on people anyway.. at best you arn't giving them even more, at worst, you are making yourself look really damn guilty[tm]. It's just one of those things that's interesting to contemplate.