a 1″×8″ board at least 5′ long.
Note
Pine is cheaper and easier to work than a hardwood like oak (for some important notes on wood sizing and selection, flip to About Board Sizes in About Board Sizes).
a dozen 1 1/2″ wood screws (for building the box)
about three dozen 3/4″ wood screws (for mounting hardware to the box)
a variety of locks and latches (I’ve used a barrel bolt, a chain lock, and a window latch. These are easy to scrounge at resale shops or garage sales; if all else fails, a barrel bolt or window latch is only a couple bucks new at the hardware store, but a new chain lock tends to run at least $10 or $12.)
hinges (You’ll want to keep an eye out for a pair of narrow cabinet hinges that can close flat in order to make the double door–style lid. Since the hinges are largely exposed, it pays to choose something a little more snazzy; brass screams class.)
a few knobs (You can use these to fancy up the doors, but you’re well advised to put one on each end; a toddler is going to want to haul this around, and you might as well make it easier to carry, rather than making it easier to crush a toe.)
(optional) about a dozen orange juice can lids (These make great “coins” for toddlers—they are free, made of safe, inert stainless steel, make a great sound, have a pleasing weight and texture, and offer no sharp edges or choking hazards.)
