I bought a toolbox at Bunnings (not sure if they have Bunnings in places other than Australia.. anyway it's just a big hardware store) for pretty cheap (under $30 I think) and put a padlock on the front. I keep it in the back of my car, which is occasionally inconvenient but it makes it much less likely to be discovered than if it was in my room, so it's a price I pay gladly. A toolbox looks totally at home in the back of a car, one with a padlock on it less so. But if anyone asks I plan to tell them that I bought the toolbox with the intention of filling it up with tools, but I haven't got around to it yet. And for the time being it's just got some towels stuffed in it which are helpful for moving furniture (which I've had to do a bit of lately). Why is it locked? I found a lock floating around in my car and put it on there.. not sure why.. but I remembered later that the key was in my room and I haven't been bothered to take it off yet. Not like there's anything I'll need to get at urgently anyway.
Now that is a pretty weak and unconvincing story but that doesn't particularly matter. It doesn't matter how dodgy or suspect I look - no one is going to get into that box without a pair of bolt cutters. If someone gets really suspicious about this, I can always move my stash somewhere else when I get the chance. I used to hide things in cardboard games/console boxes in my cupboard.. when I think about that now I can't believe how reckless I was. It just takes one bit of (admittedly, very) bad luck and I'm busted. Way more peace of mind with a metal box, a lock, and a card to hide it all in.