Here are the official rules of what you can and cannot bring into Mexico as a tourist, from the Sonora Tourism web site.
2.5 What is customs and what do I have to do?
In Mexico, customs is the authority responsible for the tax payment of goods and vehicles that enter and exit the country, and one of their duties is to inform you about the taxes you must pay in order to bring goods, money, or vehicles inside the country. As you go through customs, you must declare if you bring with you any goods other than your personal belongings so you can pay the resultant taxes.
2.6 Which goods are part of my personal belongings?
Your cloths, shoes, personal hygiene products new or used, a camera, a video camera with batteries, 12 films or video cassettes, binoculars, cell-phone, pager, typewriter, computer new or used (laptop, notebook, omni book, or similar), and portable printer, new or used. You may also bring in as part of your luggage a camping tent and gear, 4 fishing canes with accessories, two used sports equipments that you can carry on your own, a water surf board with or without sail, a portable or mixed sound reproduction equipment, 5 laser discs, 5 DVD and 20 CDs or audio tapes.
Also considered part of your personal luggage are a music instrument that you can carry by yourself, books and magazines in such a number that it would not seem they are for sale, 5 toys that you can carry, pharmaceuticals for your personal use (in case you need psychotropic drugs a written medical prescription is required).
Handicapped individuals may bring any personal goods they use to help them diminish their disability; adults 18 years old and older may also bring up to 20 cigarette cartons, 25 cigars, 200 grams of tobacco; as well as 3 liters of wine, beer or liquor.
2.7 What is a “franchise” and how much am I entitled to?
Is the benefit free of taxes for goods you introduce into the country. If you arrive to Mexico by plane or ship, you may introduce one or several articles apart from your luggage, up to 300 U.S. dollars, or its equivalent in other currencies. If by car or bus, the franchise is of 50 U.S. dollars per person, including under age, as long as they travel in the same vehicle. This franchise does not include additional alcoholic beverages, tobacco or additional gasoline for your vehicle.
2.8 How much do I have to pay for goods additional to the personal belongings and franchise?
If the cost of your goods exceeds the franchise but is under 1000 U.S dollars or its equivalent in other currencies, you must pay 17% of the total value, and fill in the “foreign commerce contribution payment” form. If the cost of your goods excluding the franchise is over 1000 U.S. dollars or its equivalent in other currencies, you must hire the services of a custom broker, for the importation procedures. (ask at customs where to find it).
2.9 How do I go by inspection at customs?
Not relevant to drivers.
2.10 What is not allowed to bring into Mexico?
You must not bring into the country, in your vehicle or among your personal belongings, fire weapons, bullets, explosives, and related chemical substances. Also forbidden are recreational drugs, narcotics, psychotropic and other illegal substances or vegetables.
You must be aware that the elaboration, preparation, sale, purchase, supply, transportation, introduction or removal from the country of any of the previous products is a crime punished with 10 to 25 years in prison.
2.11 What is forbidden to remove from Mexico?
Removing archeological treasures, documents, and historic objects belonging to the national patrimony, and wild plant and animal life without the appropriate authorization is forbidden.
2.12 How much money in cash or checks can I bring into Mexico?
Bringing any amount of money is not a felony, and you do not have to pay any taxes. However, if you bring more than 10,000 U.S. dollars, but under 30,000, or its equivalent in other currencies, you must declare it at customs. If you neglect this action, you will be penalized by paying 20% to 40% of the amount in excess of 10,000U.S. dollars; if the amount not declared is over 30,000U.S., dollars you will be turned to the appropriate authorities.