Swiss Army Knife.
Hammock. Lots of budget hostels charge half the price of a room for hammock space.
ClothesWhatever clothes you bring, make sure they’re synthetic and light. It’s so humid in Nicaragua that clothes never dry. It’s so hot that you won’t need many clothes.
Flip-flops (chinelas). Light, easy to pack, and useful, especially when using less-than-hygienic bathroom facilities.
Rain gear. Particularly a waterproof pack cover and a raincoat. It the rainy season (May-November), it rains heavily at least once per day.
Sturdy hiking shoes. There are lots of good volcanoes to hike.