Modern life has made checking in for your flight a whole lot easier. Thanks to the Internet and smartphones, you can now check in up to 24 hours beforehand and have all of your travel documents ready before you even get to the airport. Online check in typically involves logging in to the airline Web site and entering your reservation number and printing out your boarding documents. Or if you have a smartphone, many airlines have apps that allow you to check in on the go, without even the need for a printer. Simply hit a few buttons to check in and an electronic version of your boarding pass appears on your screen. If you heed our advice to travel light, then you can avoid the check-in process altogether and go straight through airport security and to your gate.