Comment 4th, 5th, 6th Amendment Wallet Cards to carry (Score 3, Informative) 156
NORML's is here, and another one from a lawyer is here. Well worth printing out and laminating and keeping in your billfold.
Two things to note: 1) If you happen to be on a military base, even just to turn around and leave because you made a wrong turn, your rights are severely abridged. If you are on their property the military is free to search anything they want.
2) The War On Drugs has created a lot more room for officers to manuever in if the key phrase "drugs" is used. Here is a rather disheartening discussion about this "special" area of search law.