If I'm just carrying around town, it's 5 in the 642 and 7 on the speedloader (12 total, only because 8 don't fit in the simply rugged pouch). There's also a 15+1 9mm in the car with an extra mag, if I need it.

If I'm on foot and away from civilization, outside of town hiking or whatnot, either the 9mm with extra mag (30 rounds), or the 686+ with 2 moonclips (21 rounds) are on the belt.

It doesn't hurt to carry more than enough ammo, but I'm comfortable with just my little j frame. Extra ammo is no substitute for situational awareness and using your brain.