Crackers are made specifically for nitrous use. They can be found at head shops and similar stores. Crackers come in metal and plastic, and a variety of colors. The metal crackers are primarily silver and gold, but sometimes anodized black. People don't seem as personal about their crackers as they are about bongs.
Balloons are easy to conceal and carry.
Finally, unlike masks, should you pass out, balloons will not stick to your face. Unfortunately, balloons also have many shortcomings. The primary problem is that the intense cold from the gaseous expansion freezes the balloon and eventually ruins it. Standard party balloons do not last more than ten times. There is an art to releasing the gas slowly and warming the balloon and cracker.