Oh, I forgot to say. I once came home to find my mum emptying my drawer. She’d decided to put the stuff under my bed. At the bottom of that drawer was a packet of cigerettes and a lighter. God knows how but I actually managed to grab them before she saw.
I also ripped up my pill perscription and put it in the bin. My mum stuck it back together to find out what it was.
Nothing was safe.
I used to hide stuff - money, certain magazines - in a hollowed out speaker cabinet. Speakers were long broken, so I just unscrewed the front and ripped out the innards. Worked well for a while, but then I moved rooms and got a larger closet, so it wasn’t necessary anymore.
We’re all so creative as teenagers, aren’t we?
I used to be required to do the laundry for the entire house (6 of us) I was sick of 4-5 loads a day. So once I hid the laundry in my drop ceiling (my room was in the cellar) I don’t know how my father found it…but he did. He moved the white tile and <plop> laudry appeared.
I hid stuff under the mattress.
In my locker at school.
I used to be required to do the laundry for the entire house (6 of us) I was sick of 4-5 loads a day. So once I hid the laundry in my drop ceiling (my room was in the cellar) I don’t know how my father found it…but he did. He moved the white tile and <plop> laudry appeared.
I hid stuff under the mattress.
In my locker at school.
Correction: No one’s commented so far :).
I used to “hide” things in my desk drawer, telling my mother not to open them because they were private. She didn’t (or, in accordance with the point I made above, didn’t let on that she did).
I was doing my own laundry well before I had anything to hide, so my closet and dresser were/are both secure places. Also, I’ve never had much to hide, and my parents aren’t particularly nosey.
I never had to hide stuff from my folks–they were big believers in privacy and personal space. My brother, OTOH, had an obsession with finding out what his Christmas gifts were ahead of time, so I had a couple of good hiding places for the purpose. For small things, I hollowed out the top foot of one of my bedposts and modified the cap of the post to latch in place–you couldn’t just unscrew it, you had to know how to open it. I took advantage of a split piece of paneling in my room to make a sliding panel and hid larger items inside the wall.
Eventually, my parents started asking me to hide all of his gifts. 
When I was a kid I thought I was smart because I had this pony which had a locked compartment, and I would keep my money in there. We were at camp one summer when my house got broken into. So I had money in that pony and I was all worried that somehow the burglars had taken it, so I was still at camp and my Mom phoned to tell me about the break in, and I asked er to check if my money was still in the pony. So yes, duh, there went my hiding place. LOL.
My best friend started taking the pill against her parent’s wishes (they thought it would encourage her to have sex…but anyway…), to hide it from them she kept the pills in an empty mini M&M’s container thing.
Anything I need to hide I tape it under a shelf or a desk or something if it’s relatively small/light, and otherwise it’s burried in my closet.
I hid small things in clean socks in my sock drawer. My mom was so close the whole time and she never found out. I think.
I used to have some pretty cool stash places:
I had a round metal case (about twice the size of a CD and about 3 inches high) which fitted perfectley into the bottom of a pot that I kept a plant in, you could pull it out roots and all very easily with no mess so I cut off the bottom and replaced it over the tin.
I also had bear floorboards and found a place under there I could hide things. But my most conveniant stash was to simply put things in the pockets of an old jacket that was hung up at the back of the wardrobe…no one ever looked there.
Geez, I thought the rugs were bad enough.