Waterproof Poncho
In the UK it rains, so you need a waterproof poncho or hooded rain cape to keep yourself dry. These can be carried when not needed often in a small stuff sack in your pocket or rucksack. Then when it rains can be worn over your normal jacket or clothing. If your waterproof poncho is dark olive green or camouflage pattern it can also double as extra camouflage, perhaps when hunting or wildlife watching.
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Wikipedia says:
When you pack a backpack or tote for whale watching, put in the obligatory sunscreen, a hat or visor, a sweatshirt or sweater, and a waterproof windbreaker, poncho, or jacket.
Definition: a blanket like cloak with a hole in the center to admit the head, originating in South America, now often worn as a raincoat
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