The brims are made of plastic rescued from the packaging for a dress shirt. Other possible sources are plastic spiral notebook covers (not the cardboard ones, though) or blister packaging if the product is big enough to have about 6" x 4" of flat (or gently curved) plastic. The smaller brim would probably fit on a plastic milk or juice jug.
The orange one has a zipper on the crown under which you can put any kind of Sekrit Surprize. The zipper was part of the neckline of the original shirt, which I cut to fit. I also like to put pockets on the crown, as I did with the brown one.
This tutorial shows the construction of the brown hat as I'd already made the orange one. However, the technique is almost exactly the same for both, just the pieces are slightly different sizes.
Step 1: Materials and tools
You can of course also use yardage. You need about 2 or 3 square feet for either hat, which is usually not more than 3/8 of a yard. One shirt would be plenty, I used two only because I wanted a contrast.
I suggest using a lining so you don't get bits of thread in your hair whenever you wear your hat. If you have enough, and it's not super heavy, you can probably use your main fabric. An old t-shirt works well too.
I mentioned the plastic for the brim in the intro. You need some of that.
Finally, you need about 4 or 5 feet of quilt binding, which is like very wide seam binding, an inch wide. It's available in packages of 3 yards in any fabric store. You can substitute another piece of fabric the same dimensions as the band, but I find quilt binding is easier and faster.
Finally finally, you need thread and a sewing machine. No special stitches are required, any old sewing machine will do.