I bring 150%. Most I've ever seen is when a shooter had to do two reshoots at a 5 stage match. He actually did run out of ammo and I gave him some of my factory stuff.
That's the thing, if you are shooting 9mm, .40, or .45, chances are that someone will let you have/borrow ammo if you need it. It might be reloads (scary), but you'll have ammo. Hell, I've even seen people offer entire guns, mags, belts, and ammo to folks who forgot or had other gear issues.
What a great sport.