Pack a light rain jacket, shoes that can get wet, and reef-safe sunscreen. In the Pacific dry season, December to April, you can skip a heavy shell. You still want the light jacket. Valley nights usually sit around 18–26°C. The beaches commonly reach 28–32°C and do not cool off much after dark. The cold exception is Monteverde, and the summit of Chirripó.

Five quick-dry shirts, two shorts, one pair of long pants, two swimsuits, and shoes you can walk a wet trail in. Add sandals for the sand, and water shoes for waterfall rock and a rocky entry. A hat matters by noon. Shade on the Pacific beaches is thin. A light layer, a fleece or a thin sweater, covers valley nights and a Monteverde morning. A rain jacket beats an umbrella on a boat and on a trail. Cotton stays wet once a shower starts at lunch. Leave the heavy coat and the jeans.

Reef-safe sunscreen is the one to bring. Some parks do not want the other kind in the water. Bring insect repellent for the Caribbean and for wet forest, and less of it for a dry Guanacaste beach at noon. A small dry bag keeps a phone alive on a boat day. The month you are matching is in the best time to visit.