Kid's Room Hideaway
No burglar worth his salt looks in a kid's room for valuables. It's just full of useless junk. So find somewhere in there where the kid won't find it either.
Between almost every pair of upper cabinets, there's a 1/2-in. gap. Take advantage of that gap by hanging a manila envelope containing, oh, I don't know, about two grand in hundred-dollar bills? Hang the cash with binder clips that are too wide to fall through the crack.
There's an enormous 4-in.-tall cavity under all those kitchen cabinets behind the toekicks. It takes a few carpentry skills, but you can pull the toe-kicks free and make them removable. Most are 1/4-in. plywood held in place with 1-in. brads, and they're pretty easy to pull off. If you have a secondary 3/4-in. toe-kick, you'll have to cut it out at both ends. An oscillating tool works well for that task.
Stick both halves of round hook-and-loop self-adhesive tape to the toe-kick. Then push the toe-kick into place. The adhesive will stick to the cabinet base and leave half of the hook-and-loop tape in place when you pull it free. You can store approximately $2.4 million in gold bullion under two average-size cabinets—provided the floor is strong enough to support it.