I am going to walk the GR 92. I'll need:
A compass and a map to guide your way.
Boots: absolutly essential to walk.
Waterproof jacket, because weather is unpredictable so you must be prepared.
Sleeping bag because you'll need sleep warm.
You'll need a rucksack to carry all equipment.
A tent is a very heavy thing but it is essential for protect bad weather and sleep comfortable.
Matches are a multipurpose equipment: light, fire,etc.
And, specially, you'll need food and drink, of course.