The best time to get through the border (either southbound or northbound) is obviously when everyone else is not there. Please check our Border Wait Time info as well. Other than changing your vacation days, here are a few tips...
Check-in time at most resorts is at 4pm, but that doesn't need to limit you! Can you be an early riser? Leave Phoenix/Tucson as early as possible in the morning. When you get to town, you can do a partial check-in at your resort to get wristbands and enjoy the amenities. Bring your bathing suits in a beach bag so you can change in the poolside restrooms and start your vacation asap! If you're really lucky, your room might be ready and you can get your keys!
On the same note, check-out time is usually at 11am. This makes 11am-12noon the busiest time to hit the border northbound. Even though you have to vacate your room, you can still hang out poolside and enjoy the resort for a few more hours! Rinse the chlorine off at the open showers, change into comfy clothes, and pity the poor drivers waiting on the long line at the border. Have a late lunch in town and get back home in the early evening.
Have everything you need ready to go. A friend of mine has a "Peñasco Pouch" (or just a ziplock bag) in which she keeps her passport, copy of car registration and Mexican insurance, her trailer title, and any leftover pesos from the previous trip. It's always easy to grab and easy to have everything she might need to show the border guards. This would include the title/registration of anything you're towing like an ATV, boat, etc., paperwork for your pet, and any receipts of purchases you're bringing with you.
Familiarize yourself with the charts of what is permissable to bring into Mexico with you. No meat or meat products, no fruits or vegetables, and absolutely, positively no guns or drugs. Will they definitely go through your cooler? No. But if you say you have nothing prohibited and they decide to check and find some steaks in your cooler, be prepared for a very thorough inspection. Not worth it. Besides, Sonoran beef has a reputation as being wonderful!! It's also generally lower in antibiotics, hormones and other additives. About 75% of cattle are able to free graze, not raised in CAFO environments.
When coming back to the US, have proper documentation (please also see our passport page) for everyone in the car, have everyone remove their sunglasses, and answer all the questions the border patrol asks you. Can they deny you entry if you don't bring your passport? Technically, yes (at least temporarily). Will they? Probably not. Will it delay getting home? Yes, absolutely. Just get a passport or passport card or enhanced drivers' license and enjoy the rest of your drive.
They'll probably only ask a few basic questions like "Where did you visit?", "How long were you there?", "Are you bringing anything back I should know about?" You are allowed to bring up to 50 pounds of shrimp back to the US tax free, but no other meats/fruits/vegetables/plants. You can also bring back 1 liter of alcohol (per adult over 21) tax free. According to the US Customs and Border Patrol, you can bring back $800 worth of purchases (including the alcohol) tax free. Products made from endangered species (sea turtle, etc) are prohibited.
Let me reiterate the biggies again: Please DON'T bring back any illegal drugs, steroids, or other legal drugs for which you don't have a prescription. Don't bring back any guns, ammuntion, or switchblade knives.
Please DO bring back great memories, photos, and stories to savor until your next visit.