Here is a suggested packing list for a trip on the Inca Trail:

• Backpack (with a capacity of at least 40 liters)
• Sleeping bag (rated for temperatures as low as freezing)
• Sleeping pad
• Tent (if camping on the trail)
• Warm clothes (including a jacket, fleece, and thermal layers)
• Rain gear (jacket and pants)
• Hiking boots or shoes (with good traction)
• Waterproof hiking socks
• Water bottles or hydration system
• Water purification tablets or filter
• Headlamp or flashlight
• Sun hat and sunglasses
• Sunscreen
• Bug repellent
• First aid kit
• Personal hygiene items (toothbrush, toothpaste, etc.)
• Camera
• Passport and original ISIC student card (for student discounts)
• Emergency contact information and photocopies of important documents

Please note that the List is a general guide and you should also consider the weather conditions and your personal preferences, also some items could be restricted for taking them with you on the trail. I recommend checking the specific regulations for the tour operator you are going with.