Pack from the itinerary, not from every possible situation. Check the forecast, list the activities you actually expect, and choose pieces that can be worn more than once.
Keep documents, medicine, valuables, and one basic change of clothes where you can reach them. A compact charger kit and reusable water bottle solve more problems than several just-in-case outfits.
Before closing the bag, remove anything that has no specific use. Leave a little space for food, a damp layer, or something you pick up along the way.