Especially for an urban environment, I've always favoured a multi-tool as opposed to a single bladed knife.

Recently, I've switched over to a more minimalist tool that fits great in the pocket; a Victorinox Alox Cadet. It is slimmer than my iPhone and has a good, basic tool set. I paid $26 for mine. I believe the blade has a cutting edge of just over 2".

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Victory awaits him who has everything in order — luck, people call it. Defeat is certain for him who has neglected to take the necessary precautions in time; this is called bad luck. Roald Amundsen