i always like a second body, the same body as the first.
it is both backup and user, depending on the moment.
i prefer not to change lenses when shooting, if possible, and so a second body helps that along. i normally have the 15 on one body and then something longer on the second, like a 40 or the 50. if using one body (most of the time) i will likely have the 15 on it, and something like the 35/40/50 in the bag as well.
today, i have one body with the cv 28 on it.