See e.g. resources/mw.(units|canvas|Log|UtilitiesTime|ErrorDialog).js, most things in the resources/jquery directory, probably some of the stuff that's in the transport libraries, and so on. We could almost certainly put them in their own modules, maybe load them conditionally (if firefogg isn't enabled, why load the bloody library?), maybe even pull some of the more useful things into core and/or delete them in favour of the existing core utilities.