I use one of these metal ones: This is pretty much the same thing on Amazon. They are durable as heck, I can have it loaded up with all sorts of papers I might need. I can fit all of my pens and such. It's a little bit bulky, but it's perfect for my needs. Plus, I know I won't break it when I do run out into the field. Mine may not be the exact same brand as the one on Amazon there, but it looks the same. I picked it up for about $15 at Walmart.