If you're going to be packing it with you in your vest, you'll want something small, light, and durable. Go with a Canon. They have aluminum casing so they're very durable, they're picture quality is second to none, and they make the smallest cameras in the industry.

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Depending on what size/price you want, I'd go with the Powershot S30 or S40 or the slightly smaller S230 or S330.