This Instructable shows how to modify a boonie hat to have a zippered secret compartment on the inside.
I got the idea to have a secret compartment in a hat from an episode of Survivorman where a guy pulls a hook and line out of the zippered compartment on his hat. I tried looking online to buy one for myself but didn't have much luck finding any so I decided it was time to make one.
Making the hat is very easy, it's deciding what to stash in the zippered compartment that's the hard part. I put all kinds of survival gear in mine like a fishing hook, line, matches, pocketknife, sunscreen packet, etc. I also add a length of paracord around the hat as Stormdrane teaches in his Instructable http://www.instructables.com/id/Paracord-Chain-Sinnet-Fast-Deploy-Boonie-Hatband/