Pack for the plan, not every possibility
Read through the itinerary and add what each activity genuinely needs. Check the forecast close to departure, then remove speculative extras that only add weight.
Organise the list by category
Group clothing, documents, toiletries, electronics and medication so it is easier to spot omissions. Keep passports, tickets and essential medication in a final must-check group.
Assign shared items clearly
Families and groups rarely need one charger, adaptor or first-aid kit per person. Decide who is bringing each shared item and let everyone see when it is packed.