I carry a multitool (a Topeak something or the other, with chain break tool), but it seldom gets any use. I bought it mainly for touring. If you do buy one, test it on the bike at home. My bikes have a couple of Allen screws that I cannot access with the somewhat clumsy multitool. Also, you may need to hold a bolt in place while loosening/tightening the screw, something you cannot do with a single multitool unless it breaks into two separate tools (and the tools you need are conveniently on separate parts).

--J