RVCircus -- you do absolutely need passports, passport cards, or enhanced driver's licenses. Do not cross without one of them. The one exception is for children under the age of sixteen; a birth certificate is acceptable for them.
I would recommend getting full passports; if you ever wish to fly to Europe or elsewhere overseas, you'll need to have a full passport. If your state does offer enhanced driver's licenses, though, that may be a good bit quicker and less expensive than a passport. (It seems that currently Vermont, New York, Michigan, Minnesota, and Washington are the only states that have EDL programs.)
The NRA sticker should pose no problem, assuming of course you are actually complying with the appropriate firearm laws. Many people cross the border daily with all sorts of bumper and other stickers. Of course, you should adhere to the applicable firearm laws themselves.