The obvious day trip is across the Río Paraná to Corrientes — older, prettier, with one of Argentina's better riverfront walks and a strong Carnival tradition.
Further afield, the Parque Nacional Chaco, 110km north-west of Resistencia, protects a sample of the eastern Chaco landscape — a transition between savanna and dry forest, with monkeys, capybara and excellent birdwatching. Bring your own transport; there is no public bus to the park entrance. The Reserva Natural Provincial Loro Hablador, further west and harder to reach, has a real chance of seeing peccaries, anteaters and possibly puma.