I've been somewhat paranoid about this as well, so here's how I store it:
I have the FT lipo bag that I got when I bought my Sea Duck and power pack. I've thrown my batteries in there, and then put it into a metal ammo box.
Now, is this 100% safe? No. Lipo bags are fire resistant. The threads used to stitch the bags closed can burn, and the bags can come apart. The rubber grommets in the ammo boxes can melt from the heat of a lipo fire. All that said, it's better than leaving the batteries out and exposed on a wood table where they can cause a fire.
One of my club members recently lost his den due to a lipo battery that he forgot was charging; the battery went up while connected and took off, ruining his desk. He was able to get it put out before it took out his home, but the entire den and about 30 planes that he had went up in the process, and there was smoke damage throughout his home.
I myself recently had a close call with a bad lipo; I won a plane at our annual raffle & auction last week Thurs, and it came with a 2s lipo. I charged it up, connected it to the ESC in the plane, and it smoked the ESC and the battery immediately started getting hot and puffed. I was able to get the battery unplugged, but it was still pretty hot. I threw it in a lipo bag, then into a fire bucket that I use for ash from my fireplace, and then put the bucket IN the fireplace with the flue wide open. I figured if it was going to go up, the fireplace would be probably the best place for it - the smoke would hopefully draw out the chimney, and the brick and mortar of the fireplace wouldn't burn. The battery didn't ignite, but needless to say, I don't trust it and am in the process now of getting it discharged with a light bulb on it. Once it's dead, I'm disposing of it - better to be safe than sorry!