The bottom part of my bookcase was covered up by a loose board, that I could turn to reveal the space underneath. My parents never searched my room or anything, it was just to be safe.
I never really had contraband, except cigarettes which I hid in the shed in a space between the bikerack and the wall. My dad is a non smoker of the reformed/evangelical sort… and he hated cigarettes and their smell so much I was convinced that if I ever brought them into the house I wold be found out immediately.
So after I had a cigarette, I would first douse my self in hairspray (hell it was the 80’s most of my friends carried industrial-sized cans in their saddlebag purses) then make sure I walked around with my jacket off to air myself off before going home. Living in Northern Ontario, I was a non smoker in the winters.
My younger brother on the other hand hid everything more or less in plain view. My parents barely drank so he would put bottles of alcohol on the shelf in the basement where my parents kept their alcohol, tucking it behind canned goods and other stuff nearby. If the bottles ever got discovered, how could my parents get upset about finding an extra mickey on their alcohol shelf?
He kept all his tapes in shoe boxes, and also all his contraband. Finding anything in the 2 dozen or so shoe boxes on his shelves and dreser was like the warehousescene in Raiders of the Lost Ark.
Lucky you. I used the space under the bookcase too. Only, mother found my stash of (bad) writing.
I’d seen some really neat reflections in water, and wrote a story about someone who jumped off a bridge after looking at really neat reflections in water. Mother found this story and, naturally, assumed I was planning to kill myself - she made me talk to the school psychologist and everything. Whoops!
I wised up and started hiding things in the old toy box in the basement instead. 
My very first Playboy, the Bo Derek issue, purchased when I was not yet 18!, was stored in an old back pillow (with a vibrator with a cord!) that had a zipper. Up on a shelf in the closet. My brother, with whom I shared a room, never found it or knew I had it. Just called him up and asked.
Didn’t Iron Maiden have a song about “reflections in a pool” called “NIghtmares” or some such? Similar.
Ah yes, it was “Still Life”. Cool tune.
I didn’t really hide my porn too well… Just 3 ratty Hustlers in a Topps baseball card case under my bed. Mom found it one day, but dad put it back and told her not to say anything. I only learned this a couple years ago after I taught dad how to clear the browsing history and cookies on the computer so mom wouldn’t see the sites he’d been going to. 
I grew up during the transition from printed porn to FTP, IRC sites and other early internet porn havens. I had a bad record hiding printed porn. I deserved it because I was lazy about it, hid it between the boxspring/mattress, or else between my bedframe and the wall. My mom confiscated at least 5 porn mags from me, hidden in those locations, but she only brought it up to me, in person one time. That’s why I was lazy, because the only porn she found and confronted me on was a quite graphic (rightly so, but in my defense porn is porn when you’re underage, and I only got it from my friends brother, lol)
Once I figured out how to work FTP/IRC protocols and stuff, well there was no way my computer ill-literate dad was gonna find out, and though my mom knew computers pretty well for the time (95-96ish), the internet confused the hell out of her.
For non-porn contraband, my bedroom floor was conveniently built up 3 inches off the cement basement floor (it used to flood sometimes, the raised floor was to protect electronics). I’m a skinny dude, I could squeeze my arm about a foot into that 3"x 8’ deep space at the entrance of my room no problem. That stash was never discovered.
Honestly, there’s probably still a lot of contraband down there still today. A lot of the stuff I stuffed under there got pushed back like 3’ deep, I couldn’t even reach it with a coat hanger.
That’s priceless.
[Igors dad]“What the hell are you doing in the bathroom day and night? Why don’t you get out of there and give someone else a chance?”[/Igors Dad]…[sub]you really can find anything on the internet[/sub]
One of the benefits of living in a trailer. Floor mounted A/C vents. Lift out and room for anything that fits through a 4x12 opening. Being at the end of the house meant that I didn’t have to worry about air flow further on.
Porn was easy. Just stack it on the bookshelf and put a couple of Popular Electronics mags on top.
I didn’t need to hide porn; my father had a “lending library” - one with the softcore stuff in his bathroom magazine holder and the more salacious stuff was locked in his darkroom. I don’t recall having much in the way of other contraband that was actually kept around. Maybe some consumables, but they didn’t last long.
I had a big stereo/dual tape/turntable/cd player cabinet unit type things. I took the screws out of the turntable and hid everything inside of it. No one ever suspected a thing. Best hiding spot I ever had. It had a ton of space. I could have fit 10 cartons of cigarettes in there if I wanted too, but normally it was just a few packs, a couple of lighters and bag and a bowl and that was it.
Next best spot was behind the headboard of my bed. I taped a fork behind the headboard, near the top with the tines sticking outwards. Then I took a pencil case and put a string from one end to the other (like a purse strap). All I had to do was reach over my head and grab it, get what I need and hang it back up.
After that was under my dresser. It had a base molding (as opposed to 4 feet), but only on three sides. So I could reach behind it and tuck things under it.
For quick hides (lighters, individual cigarettes that I grabbed from dad and would be smoking the next day) I put them above the molding inside my closet door.
What is a “foot locker”, apart from a sports shop?
Oh, one more. My favorite. My parents house has a fireplace, at the bottom is one of those little doors that I presume is for cleaning out ashes and stuff, I found out one day, that it is almost constantly pulling air out (yeah, I was watching Mary Poppins) due to the breeze over the top. I spend A LOT of my teen years sitting in a dusty workshop smoking cigarette after cigarette and bowl after bowl there. Normally I’d wait for my parents to go out (or at least to sleep), but even if they were upstairs watching TV, I never had a problem.
I did, however, find out that for some strange reason, when it’s humid outside, air actually comes INTO the house. In fact, on those humid days, the main floor of my parents house smells like a fireplace. Never could figure out why that happened. I tried to fight it once. I was annoyed that I was gonna lose a day of smoking down there over this so I setup a fan in the hole. Well, with the fan blowing air up, and the humidity forcing air down they met in the middle and all the smoke got sent out the fireplace onto the main floor. Luckily, it was just my brother and home and he let me know right away.
A big chest you keep by the foot of your bed.
My porn went into the space between the mattress support and the drawers.
Later I had to hide pretty much everything I wanted from my siblings: cash (I was the oldest and first to get a job), candy (I was the only one who had money), bus tickets (my brother would steal & sell them), video games (on old systems sometimes you only had one save slot, and my brothers would deliberately ruin my saved games), etc. I had to get really creative, to the point where I would sew long loose threads into the curtains to use as a harness to hide stuff.
My bedroom was in the basement, which had a drop ceiling with big styrofoam tiles. Everything went up there.
Hmm…haven’t though about it in decades, but I wonder if anything is still stashed up there? I’ll have to take a look-see next time I visit mom.
Joints were kept in the curtain rods covering my windows.
Porn was stashed under the bed (not the brightest idea, admittedly, but I wanted to have it close at hand harumph!). Fortunately, when my mother inevitably discovered my porn stash, her first reaction was to audibly say, “Oh thank God!” (my younger brother was present at the time so I got a first-hand account). Apparently Mom had been worried that her bookish, non-sports-interested oldest son might have, gasp, teh GAY!
She never said a word about my porn to me. 
How does Barometric Pressure work?
In the attic. My Mom couldn’t get up there without a ladder, and always made me or my Brother do it. I could go up Ninja style braced between the two walls, and even made it up with two cases of wine coolers balanced across my legs once.
Wow, I haven’t thought about this in ages. I lived with my parents until I was 20. I hid my condoms, a little porn and maybe a couple joints every so often in the ductwork of my heater vent in my bedroom floor. I don’t think my mom ever found my stash. Like Hal, I hope I never left anythink there; it’s been 16 years.