Piggy-backing on the previous replies, I would add that the (to the extent possible) expected environment for a survival kit may include considerably more specialized gear than what would be carried while backpacking. Consider that the survival kit may include important documents, more medical prescriptions, and perhaps even some tools (for an urban environment) that would be inappropriate for camping/backpacking (i.e. a crowbar). Obviously, some overlap is possible and likely, but it could be dangerous to assume that only wilderness gear will suffice for an emergency. It all depends on the environment and your needs.