I hid how little time I spent studying by studying behind closed doors on top of my bed. I would have a quilt across the base of the bed under which I would shove whatever novel I was reading and have my watchtower open on my lap with a highlighter in case anyone came in. The sound of the door turning gave me enough time to do this.
When I would go on sites such as JWD the creaking of the stairs would give away that someone was coming down. In my room I would have just enough time to see someone in the doorway to minimize what I was doing. I also had a program called Quick Hide Windows that with a secret keysequence would minimize the window you were on but it would NOT appear on your taskbar, a different sequence would bring the windows back up. I would have nested subfolders with ambiguous filenames I would save my data to, or use password protected zip files.
I had bags of craft supplies in my closet I used to hide things like toy dart guns (banned in my house) in. I also had notebooks I would hide in the middle of school binders in the corner that had notes on religion and other such things.
I also used to sneak downstairs and secretly tape movies I would not be allowed to watch and then get up early and hide the tape before my mom got up. When she left for work I would have 10 minutes to start watching it, another 15 minutes at lunch and sometimes 10-20 minutes after school before anyone came home. I used to stay up to watch things on TV as well and always had another show on channel return. I would sit really close to the TV and turn the volume all the way down so it could not be heard outside of the room.
I would make separate trips to the library to check out books and then hide them in my desk or locker at school. After a party in grade 12 I also had rum and coke in a bottle hidden under a dresser in my closet for a while. I didn't want to get rid of it because I didn't know if I would be able to find someone to buy more before the next party or not but I was worried mom would find it. It was actually a coke bottle though so as long as she didn't smell it...
I had a pentagram necklace I used to wear under my shirt as well. I would hide it in one of my desk drawers in a box of sidewalk chalk when I wasn't wearing it. I never dared to wear it visibly. I did wear my rainbow freedom rings though.