Gather the backpacks dropped by monsters:
• Book Backpack
• Buggy Backpack
• Changing Backpack
• Deepling Backpack
• Ghost Backpack
• Jewelled Backpack
• Lilypad Backpack
• Moon Backpack
• Mushroom Backpack
• Peppermint Backpack
• Pillow Backpack
• Winged Backpack
• Wolf Backpack

Gather every resistance-granting trinket:
• Bone Fiddle — quest item from the Secret Library (Asuras)
• Conch Shell Horn — combine a Wooden Mouthpiece with a Conch Shell (no quest needed)
• Ink Trinket — any variant, dropped by Sir Leonard
• Lit Torch — dropped by the Darashia bosses: Katex, Sress, Utua, Yarikas
• Moon Mirror — buy a Mirror from Black Bert and catch moonlight with it
• Scarab Ocarina — pull an Ocarina from a chest and use it on a slain Scarab
• Starlight Vial — buy a Vial from Black Bert and catch starlight with it
• Sun Catcher — buy a Catcher from Black Bert and catch sunlight with it

Crafting the backpack costs: 100x Silver Token, 100x Gold Token, and 10,000,000 gold.

With all the backpacks, trinkets, and payment in hand, head to Camilla at Targuna (right above the depot) — she'll craft the Adventurer Backpack for you.