Packing

How does one pack for 8 or 9 months abroad?? That is our current challenge. We started spreading our all our belongings upstairs today. We think we're going to get 2 checked bags a piece free of charge. So that is good... but the space goes quickly... towels, winter coats, clothes, shoes, sweaters, kitchen supplies, books, toiletries... and there is so much more! Any world travelers have any advice on packing for longer trips? Any must-take items?