For Ranger School, this is an optional item, and you should bring at least one box. Bringing these is an absolute must.
For Sapper Leader Course, this is a mandatory item, and you need to bring at least one box.
For SFAS, this is an optional item, and you should bring at least one box. Bringing these is an absolute must.
The cadre at Ranger and Sapper should give a class on how you should pack your ruck. Basically, you will line your ruck with a trash bag to keep your gear dry when you're crossing streams or if it rains. Don't bring lightweight, flimsy bags. Bring contractor bags that are at least 3 mil thick. These bags have maximum puncture and tear resistance. These 42 gallon contractor bags measure 32" x 50" and fit perfectly inside a ruck. It is a 25-pack roll of 3 mil bags. Flat seal bottom keep your gear in and the moisture out.