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If there is a running creek or along river banks, then crayfish will congregate when tree branches are above and insects fall. Or somehow edible detrius falls in. That is where a clever perwonncould take some window screen material and create makeshift crayfish trap aka crawdads or mudbugs.

Then you purge them in saltwater. Then you boil them up with some vegetables like corn.

You got periwinkles and limpets in the UK. The Irish used to routinely eat such food.