When cutting brisket, always slice against the grain. There's an important reason for slicing brisket against the grain, and that's because it shortens the fibers. This way, it's nice and tender instead of chewy. Not slicing against the grain can make a big difference in texture!
You'll want to use plain gingersnaps, not the kind that's iced. Don't worry, your brisket and gravy will not taste like cookies.