Ok. Here goes.
7 eleven soda cup. Wasn't my idea. Read it here on THR. Put some cloth in the bottom and a Smith 642 fit perfectly.
a Glock 27 in a back pocket of 5.11 pants. Not the brightest idea I've had, but it worked for the day I did it, before I bought a holster. I don't wear 5.11 pants anymore either. I bought one pair to try them out and wasn't thrilled. Too gunny for me. I'm a gun enthusiast, but I don't need the world to know that by looking at me.
Under my arm for short distances from my apt to the car when I lived in an apt building. I only did this for early morning walks to the car (ie: 4 AM). There was a history of violent crime in the parking lot at the time. If I was headed to school where I couldn't have a gun, instead I'd bring a 9 iron golf club. I could put it in the trunk and claim I was going to play golf later.
Grocery bag - I needed to bring my gun into a gun store to get some stuff for it and didn't want to have a case that screamed "gun" as I walked in as it's a high-crime area. Grocery bag worked. Didn't attract attention.
Guitar case to store a rifle new in box (again when I lived in an apt). I didn't want people to know I was bringing guns in (not that there was a rule against it or anything). When I bought a Ruger 10/22 (since sold) and my Savage Mark II .22lr, I put the whole thing box and all in a guitar case on the way from the car to the apartment.
The same reason for pistol cases in a laptop bag. Some were hard to fit, but my Tumi bag is expandable.
For me that's it.
My dad had one that beat any of my ideas.
When the house was built and the furniture custom built for the house, he noticed that in his office, one of the filing cabinets that had been build had extra space behind the drawers. They must have cut the wood too big for the cabinet and then instead of building bigger drawers, they just installed the rails for the drawers forward so they would look right.
He stored his gun and ammo behind the bottom drawer for years. The downside is that you'd have to remove the drawer to get to it.