Imagine arriving at a long-awaited tropical destination. What's in your bag? A bathing suit and sunscreen might be high on the list, but what about a light rain jacket and umbrella? Depending on where you're going for fun in the sun, these might be important, cost-saving additions to your luggage.
Many tropical regions owe their lush vegetation to long periods of precipitation -- monsoons or extended rainy seasons in many equatorial regions. Booking a trip during these times of year may let you save on hotel fees, since you're gambling that your visit will coincide with unseasonably clear weather. But you could eat much of that savings if your group doesn't bring clothing appropriate for the weather.
Packing a light rain jacket, umbrella and shoes that you can wear in wet weather can mean the difference between enjoying the trip and needing to find a local shop that sells these items -- likely for a much higher price than you'd pay for them at home. And investing in a lightweight but cozy cool-weather jacket (sporting goods stores have lots to choose from) can save the day in case a cold snap that wasn't on the 10-day forecast hits. These items don't take up much room in your luggage and have the added benefit of helping you get out and enjoy the destination, regardless of the weather.