Do I really need a waterproof jacket, or is water-resistant enough?

You need fully waterproof. The wind in Patagonia is strong enough to force water through fabric that is only 'water-resistant'. If it isn't rated for heavy, sustained downpours, you will get wet.

Can I rent gear instead of flying with it?

Yes. Puerto Natales (for Torres del Paine) and El Chaltén (for Fitz Roy) have excellent rental shops. It is often cheaper and easier to rent bulky items like tents and stoves than to pay for extra airline baggage.

What is the most forgotten item?

Lip balm and high-SPF sunscreen. The ozone layer is thin in the south, and the combination of wind and sun will burn your skin and lips much faster than at lower latitudes.

How to pack for hiking in Patagonia

Pack using a strict three-layer system to handle Patagonia's notorious 'four seasons in one day' weather. Prioritize high-quality, synthetic, or merino wool base layers and a reliable hardshell jacket that can withstand high-speed winds and heavy rain.

Adopt the layer system. Bring a moisture-wicking base layer (merino wool), an insulating mid-layer (down or synthetic puffy), and a windproof/waterproof hardshell. Never rely on a single heavy coat; you need to be able to strip down when climbing and bundle up when the wind picks up.
Prioritize footwear. Wear broken-in, waterproof hiking boots with ankle support. Patagonia's trails are rocky, muddy, and uneven. Ensure you have two pairs of thick wool hiking socks to rotate so one pair can dry while you wear the other.
Protect your gear from moisture. Pack everything inside your backpack in individual dry bags or thick plastic trash compactor bags. Patagonia rain doesn't just fall; it blows sideways and will soak through a standard backpack cover within 20 minutes.
Bring trekking poles. Do not skip these. The steep descents in Torres del Paine and El Chaltén put massive strain on your knees, and they are essential for keeping your balance when 60mph gusts hit you on open ridges.

Do I really need a waterproof jacket, or is water-resistant enough?: You need fully waterproof. The wind in Patagonia is strong enough to force water through fabric that is only 'water-resistant'. If it isn't rated for heavy, sustained downpours, you will get wet.
Can I rent gear instead of flying with it?: Yes. Puerto Natales (for Torres del Paine) and El Chaltén (for Fitz Roy) have excellent rental shops. It is often cheaper and easier to rent bulky items like tents and stoves than to pay for extra airline baggage.
What is the most forgotten item?: Lip balm and high-SPF sunscreen. The ozone layer is thin in the south, and the combination of wind and sun will burn your skin and lips much faster than at lower latitudes.