A chain tool is a handy tool to have if you happen to need a chain tool. Those situations come up but, fortunately, not real frequently.
A better question is "How safe do you feel you need to be?" I've provided tech support for some big rides so I've had some experience that might be pertinent.
If you can handle your own flat tires you are about 98% covered. Fortunately, flat tire fixing stuff is fairly compact to carry with you.
After flat tires, broken spokes are by far the next most common issue. That takes a spoke wrench, cassette cracker, chain whip and a replacement spoke (it's almost always the back wheel). That's quite a bit of stuff to carry with you. I've never seen one of the fiberfix spokes used so I don't know if they are a prudent fix or not. If you want to be sure of getting the right replacement spoke today, better bring your own. There's too many sizes, colors, shapes etc. today for most shops to keep everything in stock.
Third on my experience list, believe it or not, is bottom brackets. Again, special big tools and significant replacement parts. I suspect that a lot of people never do any bottom bracket inspection or maintenance.
Then comes chains, broken cables and the like.