Here are some pieces of code to put in your EMACS init file (e.g. * EMACS). Note that the dollar signs ($) should be changed to ESCAPE characters (^[), and in general ^x means “control-x” for some x.

The default Help character in EMACS is Top+H, but since you probably don't have a Top key on your keyboard, it's convenient to change it. Using ^H may feel more “at home” for modern Emacs users, but over Supdup/Telnet there is no difference betweeen ^H and BACKSPACE, which is too useful to miss.

For this item, note that ^^_ below is ^^ (control-uparrow) followed by _ (underscore).

fs %TOFCI$"e !* If you don't have Top, it's hard to press Top-H!
  128+^^_fshelpchar$'               !* so use ^_ (default is Top-H). Note you have to type it twice. !

There is no file protection in ITS, so it's easy do overwrite system files by mistake. Too easy, in my humble opinion.

!* Protection against disasters:
   By default, make all file buffers read-only,
   but undo it for home directory, HACK, and .TEMP.
   !
fs hsname$:f6[2
 @:i*/ m.m ^R Set File Read-Only$[0
      -1m0$
      fs DSname$:f6[1
      f=1^]^S2$"e m0$'
         "# f=1HACK$"e m0$'
            "# f=1.TEMP.$"e m0$'''
      ]1]0/ m.v Visit File Hook$
]2