It seems you can never have enough different sizes, shapes and cuts of files. Perhaps the most useful are a cut 4 half-round and rat tail. The cheap diamond grit nail files are handy too. I'm not sure why the razor knife and minature channel lock pliers ended up on this page, but they're useful too.

Broaches are perfect for enlarging bushings by a thousanths or less for that wiggle-free fit. You really only use one or two sizes for slot car work.