You’ve worked hard, you’ve paid your dues, now it’s time to go on a well-deserved vacation.  But don’t leave home without covering all your bases – including your beloved guitar(s).  As guitar owners, it is imperative that we remember that guitars are made of wood, not titanium.  Guitars are not invincible – they are susceptible to environmental variables, namely relative humidity.  Relative humidity is a ratio, expressed as a percentage, measuring the amount of moisture in the air compared with the amount of moisture that would be present if the air held as much water vapor as possible.  The numbers in this ratio can be altered by altitude and temperature.  Therefore, when bringing your guitar along on vacation, it is important keep in mind any changes in humidity, altitude, and temperature as these kinds of changes can damage your guitar.  For example, say you bring your guitar on a trip for two weeks.  The temperature where you’re going is 20 degrees colder than at home and the amount of atmospheric moisture is a little higher – a combination which makes the relative humidity higher than at home (since cold air can’t retain as much moisture as hot air).  You don’t play your guitar at all during the first week of your trip, but during the second week, you decide you want to jam a little bit.  You open your case, look down at your cherished guitar, only to find that the neck looks like Robin Hood’s bow.  Surprised?  You shouldn’t be.  Wood moves as it absorbs and releases moisture, which it collects and loses from the air.  This is wood’s natural response to the combination of change in relative humidity, the tension of the strings, and not being handled for a prolonged period of time.  To avoid this issue, just keep an eye on your guitar, adjust it as needed, and loosen your strings a good amount before you travel with it (to prevent string tension pressure from being amplified as the guitar is shifted or bumped during travel).  It’s as easy as that.