How do people pack clothes traveling?

How do people pack clothes traveling? How do you pack enough but not too heavy? Cuz jackets apparently are too heavy!

I’m going to japan (tokyo and osaka) at the end of the month and I need to pack for cold weather because it’s gonna be cold asf because it’s December.

I plan on packing multiple flannels and t shirts.but my dad says it’s too heavy and too much
How do people pack clothes traveling?
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