I also bought an old hat box at the flea market. I just loved that it was a square and had a window space in the front. I tried to get a price discount because of the missing window plastic (see below), but the seller said that she had just bought it on ebay and didn't really even want to sell it because she planned to use it for carting and storing her stuff. Makes it kind of hard to get a discount when they don't even want to sell it. Here it is, as I bought it. I also show a free bakery box I got at Pavillions grocery store when buying my son's birthday cupcakes. Can't really resist pink bakery boxes, especially those that have windows. Still loving Martha's.
I wanted to put something in the opening, so I used an old transparency from Artchix Studio that I had lying around. Transparencies are so nice and sturdy. Unfortunately, it wasn't quite big enough, so I sewed some ledger paper around each side of the transparency. Then I just taped it in. That way, I can see what's inside, but don't have to worry about the plastic being too sheer, like the originals often are.
And, of course, the fun part, filling up the boxes!