Package cars in the snow? They're sh*. I've probably been stuck at least four or five times in less than three years (only once officially). I'd say I've finally gotten a hang where I can and cannot go in these things, and to utilize EC if you have even a trace of uncertainty.
It's always harder when it's snowing on a new route though. I got lucky this peak though. No snow so I got to learn a new route in decent weather. Now when I do have to run this one in the snow I'll know exactly whats at the end of those lanes, where I can safely go up or down and turn around, and where to just stay the hell away from.