Are you carrying the casing, too? If so, lose it and you'll shed about the weight of a dry booger. And if it's one of those cables with two different type ends, you might want to cut off the one that doesn't fit your bike ahead of time. While you're at it, trim it to size and duct tape the raw end to keep it from unraveling. This is all assuming you don't carry a snipper with you that's capable of cutting through a brake cable.