As effective as C4 is in New Vegas, its too rare and expensive to be practical.

So here comes a revolutionary new idea.

VALUE C4!

All you need is any mine, and a silenced varmint rifle. Place the mine, then deactivate it, but don't pick it up. The rather than use a detonator, shoot it with the rifle!

If you need something bigger than a frag mine, use a fat mine! I've actually been doing this recently, it works reasonably well.