Send your girlfriend off with a bang by taking her out dancing and giving her a gold locket before she goes away on a trip. Or spend a quiet night together before she leaves and give her a romantic reason to come back home to you. You don't need to spend an extravagant amount of money on a gift for her; often the most romantic gifts are the well thought out ones.
Candle a Day
Write a note for each day your girlfriend will be away on a trip and wrap it around a candle. Each note should list one reason why you love her. For example, "I love you because you care enough to make me chicken noodle soup when I'm sick." Rubber band each note around a candle and place the candles in a box with a lighter. On the top of the box write, "Select and light one candle each evening before reading the note attached to it."
Love and Music
Borrow your girlfriend's MP3 player and load a playlist that expresses how you feel about her. Record a short message telling her to enjoy her trip and that you will see her when she returns home. The recording will be the first track on the playlist. Depending on her favourite style of music, add: "Love the Way You Lie" by Eminem featuring Rihanna, "Mine" by Taylor Swift, "Just the Way You Are" by Bruno Mars, "Hey, Soul Sister" by Train and "I Just Called to Say I Love You" by Stevie Wonder.
Shirt and a Kiss
Spray one of your shirts with a cologne your girlfriend loves and offer it to her as a sleep shirt. Fold the shirt and place a bag filled with chocolate kisses on top of it. When you hand her the shirt and chocolate, request she put on the shirt then eat one kiss before bed each night. Tell her just because you can't physically be together doesn't mean you can't be together in spirit.
In a nonchalant manner, ask your girlfriend where she will be staying while she is gone and if she will be rooming alone. Then schedule a time and date when the two of you can speak. Pre-arrange for flowers, pizza or room service to be delivered to her while you are talking. Be sure to ask her to call you if her plans change, as you may need to send her surprise gift to another location.