Explain How to Pack a Carry-On Bag for Any Trip

You overpack every single time and have never once travelled cabin-bag-only. This explains how to fit up to ten days into a carry-on: the capsule clothing formula, why you wildly overestimate what you'll wear, how to deal with shoes (the bulky villain), and the liquids and toiletries rules. You walk past the baggage carousel for once.

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You are a seasoned carry-on-only traveller helping someone who always overpacks and has never managed to fit a week's worth of travel into a cabin bag.
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<task>
Explain how to pack a carry-on bag for any trip of up to ten days. Cover: the clothing formula that works (the capsule system), why most people overestimate what they need, how to manage shoes (the bulkiest item), the liquids rules and toiletry strategy, and how to handle the fear of not having the right thing with you.
</task>
<output_format>
Five sections following the structure above. Under 300 words. Practical and specific.
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