I decided to try using a little tomato paste can covered in parchment to bake the curve piece for the top. That measured 3&1/4" long. So I cleaned out a can and took the paper label off. I cut out a pattern from cardboard that was 3&1/4" by 3&1/4" Then I rolled out my cookie dough to 1/4".
I cut out one full square for the curved top but then through trial and error decided to trim that piece down to 3&1/4" by 2&1/2" (in other words cut out the square then trim off 3/4". Place this piece on the parchment covered can (I waded up foil on either side to keep it from rolling on my baking sheet)
Next I cut out 1 full square, cut it into halves for the sides, then another 1/2 of a square for the bottom. The other half of that full square I cut in half again for the sides and trimmed off 1/4" from them to accommodate for the thickness of the bottom.
I used the can to cut out two half rounds which are actually a little less than half. So cut a full circle and cut it in half then trim off about 1/8" from each one on the straight side. Trust me when I say I did some trimming on my first one after the pieces were baked. By the 4th one I had it down to a science! So keep an Exacto knife handy. I baked the pieces on parchment for 11 minutes at 350. BUT bake all the flat pieces first so that your little half circles are cooled and solid before baking a curved piece on the can. These you have to do one at a time because you need to work with them when they are still warm but you need the 1/2 circles cool. Ok now before you bake the curved ones have some piping consistency royal icing ready in a piping bag. I used white but you could use the brown you are going to use for the icing. I also had a 4" round cookie cutter on the cooling rack to place the curved piece in while it cooled.
Ok now your flat pieces are all baked and cooling. The first curved piece comes out of the oven. Wait for about 30 seconds or so then using a hot pad pick the can up and turn the piece out into your hand being careful not to let the sides fall down and break it. Next pipe the icing into the edge curve and place the cooled half round onto that icing repeat for the other side then place the whole thing into the 4" round to cool all the way.
Repeat for the other end.
Pipe around three edges of the side piece and place it on the outside of the bottom and end pieces.
Obviously you will continue to bake your curved tops and build them as you go along.
Then I decided the yellow was too bright so I took my dark gold food color paint pen from Rainbowdust and painted the straps and hardware dark gold. I liked it much better. I also piped the kids initials onto the chest lid. I could fit 1 mini Twix, 3 Starburst candies and 7 gold coins into each one. I piped "hinges" onto the back so that the lid would stay on until they opened it to find their candy treasure.