Minecraft wiki entry for Exploring_caves, associated text: Tools - Caves house a lot of ores and other types of rock. Due to this, it's always recommended to bring a pickaxe in order to get started with anything. A shovel is also helpful for digging gravel and dirt more quickly. Axes, along with their combat utility, are also useful for quickly tearing down mineshafts for fuel. Hoes and shears may also be useful for harvesting plants such as moss blocks and glow lichen.
Offhand: a shield or bow for combat, alternatively a torch or some food.