I think carrying a BUG is unnecessary for a CCW holder. For a duty officer, plainchlothes officer, military, etc. I can see the need, as they might need to get involved in an extended firefight. However, in my mind, a CCW should really be used as a means to get the f*ck out of there and as a on-time protection item. As such, a solid high-capacity and good caliber primary should be all you need. If your main carry weapon fails and you have time to draw a BUG without dying, you probably weren't in as much danger as you initially thought or you could have spent that time leaving the situation.

Not to say that a BUG would NEVER be useful, but I find it incredibly unlikely that it's use would outweigh its annoyance and I can't recall hearing about a situation where a CCW carrier wished they had a BUG or died due to a failure of their primary. There comes a time when you have to balance convenience with carry -- obviously wearing a full intereceptor vest, carrying an AR-15 and a Glock would give you the best odds of survival in any situation you might encounter, but it's just not practical.

That said, weak side pocket seems like a pretty good choice, as far as comfort/convenience/availability. Though I'd rather put an extra mag and a flashlight in there. What are you planning to use for a bug? I'd think a lightweight .357 snubbie in a pocket holster would be a compact, reliable choice.