What is the most important gear to bring for backpacking?

The most important gear for backpacking are the backpack, tent, sleeping bag, and sleeping pad. Without these, you'll likely have a miserable experience. In addition to those "large" items, you also need to bring a pot for boiling water, a small stove, and a gas canister to power that stove. Of course, you'll need to bring food proportional to how many days your trip lasts. In some parts of the world, a bear can is necessary to prevent bears from getting to your food. These are just the most important items, and there's many more things you should bring to have a safe and enjoyable trip.