Then print-out the document checklist at right and tape it to the front of each envelope. As you acquire your passports, airline tickets, travelers insurance papers, emergency contact list, and money for tips (we take along $1us bills), place them inside the envelope. It's best to place this envelope in safe place.
Note that there are two sections to the checklist. use the top section to keep track of items as you put them in the envelope. Use the bottom section to make sure everything is in that envelope before you drive to the airport (we also run through the checklist a week before, and the day before, our trip—not necessary, but we've forgotten documents before.).
We scan our passports and documents, then upload them to cloud storage like Dropbox (a free storage site). If you lose a document in Mexico you'll be able to download proof that you did have it. You can also email a copy to yourself, or store the images in your phone / laptop.
We also make photocopies of our documents. We put one set in an envelope to leave with relatives, and take another set with us to Mexico. Make sure to write your hotel name and hotel website on the envelope so relatives can contact you if necessary.
I (Perry) actually wrote down the wrong flight time once. Luckily, there was another flight available, but it cost me money to change the ticket.
and run through the list one last time to make sure you have all your documents. We actually do this a few times leading up to our trip.