It's important to consider where you are going. What is the weather like this time of year? Will you need pants and jackets, or shorts and T-shirts? If it is cooler at night, bring a sweatshirt. If rain is expected, you may want to consider packing a poncho or an umbrella so you aren't caught in the rain. Will you be traveling to more than one location? You may want to bring a book or an music player for the flight. Try to create a detailed schedule of your trip and consider the individual characteristics of each location. Pack for the weather and pack for your comfort.
You also need to think about what it is that you will be doing. If there is a chance that you will be swimming, bring a swimsuit. If you will be going to the beach, bring sandals or flip flops. Will you be going out for a nice dinner? Bring suitable clothes for the occasion. Write down each of your potential activities and the supplies and accessories that you will need to complete them. Always consider appropriate footwear. Do not forget your athletic shoes if you will be hiking, and do not forget your sandals if you will be at the beach. Will you want to capture these activities on film? Then bring a camera or camcorder. Ask yourself these types of questions, and you will be well-prepared for your activities.
This may seem obvious, but don't forget about packing for your own needs. Write down each of the individual toiletries that you want to take. Write down the medications that you need to pack---it could be a very long trip if you don't have your prescriptions. Do you need to keep in touch with people while you are away? Pack your cell phone or your laptop, and remember to bring along the chargers for each of these devices. Do you get homesick? Bring photos of your family and friends, or even your favorite teddy bear. Consider what makes you feel comfortable at home, and do your best to create that same feeling within your luggage.