Follow the 3-1-1 rule for packing liquids in your carry-on bag. That means each passenger may bring as many 3.4 ounce (or less) bottles of liquids, gels and aerosols that can be packed in one quart-sized, clear plastic zip-top bag -- 3 ounces, 1 bag, 1 person. Liquid medications, breast milk and baby formula are exceptions to this rule. Remember, water is NOT an exception to the 3-1-1 rule.
In addition to limiting liquids, TSA prohibits packing certain items in carry-on luggage. Don't pack explosives, flammable items, firearms and certain sharp objects in your carry-on bag. You'd be surprised what fliers hope to bring with them on their travel. TSA reports having found everything from loaded and unloaded firearms, live eels, a grenade launcher, even a coral-covered explosively viable cannonball (to be fair, the cannonball was in a checked bag) [sources: Berman, TSA Blog]. It's best to verify the current list of what's okay and what's not before packing. In March 2013, for example, small knives and some sporting equipment (such as hockey sticks and golf clubs) were added to the safe list, having been banned after the 9/11 terrorist attacks. Some items are best packed in your check bags, shipped separately, or left at home.