When you are making a reentry into the United States, you should be ready with an acceptable form of photo identification and proof of citizenship. A passport can meet both of these criteria and is obviously the most recommended form of ID to have because of heightened security at the US borders. In case you don't possess a passport, you must produce a certified copy of your birth certificate or baptismal record and of course, a photo ID. A military ID, a driver's license or a state ID card may be accepted as a photo ID. In case you do not have a certified copy of your birth certificate, a U.S. state or federal government issued birth record or a Certificate of Citizenship (not an affidavit of citizenship) or Certificate of Naturalization will do along with acceptable photo ID. One should also keep in mind that laminated birth certificates and voter registration cards are not acceptable. For obtaining a certified copy of your birth certificate, you can visit the National Center for Health Statistics where you can search by the state you were born in to find the appropriate Office of Vital Records and request your certificate.

Once you approach the U.S. Customs facility, you should have all items acquired outside the U.S. handy so that you can declare them to the customs officials. These items include purchases, gifts, inherited items, duty free merchandise, repaired or altered items, items purchased for others, and items for resale or business use. It is wise to keep receipts for purchases because you may need them.

At present, the duty-free exemption for items brought back from Mexico amounts to $800 per individual as long as the items are in your possession. If the amount exceeds $800, you will have to pay the appropriate duty. In the case of families, a joint declaration is possible. For example, two people may bring back a total of $1600, which is useful if one of them brings $1000 worth of items and the other $600. The exemption in the case of mailed items is up to $200. You can best utilize the exemption if the brought-in items are for personal or household use, or they are declared to the Customs official, or if you haven't used any part of your $800 exemption in the past 30 days, or if the items are not prohibited or restricted. In the category of duty-free personal items, you can reenter the U.S. with 200 cigarettes or 100 cigars that were previously exported (usually found in duty-free shops in the foreign country). One liter of alcohol is allowed if you are above 21, if it is for your use or you plan on giving it as a gift. Any excess amount will, however, be subject to duty.

If you leave the U.S. with high value foreign items like a laptop computer, watch, camera, or CD player that you acquired in the U.S., you should register it with U.S. Customs before you leave to facilitate duty-free reentry. It will be convenient if the items have a serial number or equivalent marking. You should prove your prior possession of these items through receipts, insurance policies, appraisals, or bills of sale. The Customs officials will issue you a Certificate of Registration that will stay valid as long as you own the item. Avoid bringing back fruits, vegetables, meat or dairy products from Mexico. Money or monetary instruments worth over US $10,000 will have to be declared.