I got my federal waterfowl permit last week for crane hunting from TPW. I saw on the back there was a space that has instructions to "Attach Federal Waterfowl Stamp Here." Is that something I need to get done before I go hunting or is that something the outfitter does? If it is the former, where do I get the stamp?

That spot is on the back of every license as a placeholder for a federal waterfowl stamp. You only need one for waterfowl. It's not required for crane. But you should get one as it's not uncommon to have geese present on crane hunts. Be sure to sign the stamp across the front. You can get the federal waterfowl stamp from TPWD or the US Postal Service. If you don't get the stamp, you still need to have hip certification for all migratory game including sandhills cranes.

Yes, you don't need the waterfowl stamp to hunt sandhill cranes but you do need the sandhill crane endorsement on the front of your license. And if a mixed bag of geese and cranes is likely you need to use steel shot for both. Don't get caught with dead waterfowl and lead shot in your gun.

Best of luck and be safe!