Instead of S**t, I use Shoot or when I'm around really holy people, just so they don't think I;m saying S**t, I say Sugar!
So yeah, if your on your own, shoot is probably best. If you're with kids, Sugar is probably better.
I also use others. Here's my list of words I use:
S**t = Shoot or Sugar
B****y H**l = Bloomin' Heck!
C**p = Crud or Damn it/Darn it!
