Do your research. Check the weather at your destination before packing and use this information to your advantage. Consider how much the weather is going to fluctuate and how cold or hot you can expect it to get.
Pack your toiletries first. Remember that airline regulations prohibit you from packing more than one quart-size plastic bag of 3.4 oz. bottles, so bring what is irreplaceable, like makeup or medicated lotions, and leave behind easily purchased products like shampoo that can be picked up when you get to your destination. Pack some zip top bags, earplugs and a first aid kit into your toiletries, just in case.
Lay down a tote bag on the very bottom of your bag. You will probably want to bring home souvenirs, and you can carry them back in your tote bag when your suitcase gets too full.
Start with a towel, unless you are certain you will not need one. Towels can be extremely versatile when traveling, as they can be used at the beach, as a makeshift pillow and even as a blanket in a desperate moment. Many lower-priced hotels and hostels abroad charge extra for towels, so having your own could be a money saver.
Only pack one pair of shoes. Plan on wearing one pair of very comfortable shoes for most of the trip, and pack one extra pair of shoes for wearing out to dinner or to any special events. For women, a pair of ballet flats is a great option that does not take up much space. For men, a pair of nice loafers should do the trick.
Plan on layering and doing laundry. Rather than trying to pack a full outfit for each of the 18 days, choose some of your favorite basic tank tops, short-sleeved shirts, long-sleeved shirts and sweaters. For women, bring tights and leggings to layer with skirts and even under your pants for when it gets cold. Choose clothes that pair well with everything and can be paired together in many permutations.
Bring jewelry and accessories for nice nights instead of packing a separate outfit. You can easily dress up a sundress with a scarf or necklace and quickly go from day to night.
Buy space saver bags. If space is still a concern, you can purchase special vacuum sealable bags at most stores. To use the bags, you fill them with your clothing, and then use a vacuum cleaner hose to suck the air out of the bags. This usually reduces the volume your clothing takes up by at least half.
