They actually make units now small enough to permanently attach to the cars engine. Summit Racing sells them.
You can get small self contained units. For carrying around in a tool bag though I would get one of the 12v powered 3 cable units, otherwise Murphy says when you need it the batteries will be dead. They're usually pretty inexpensive and very reliable.
Randy Rosetta KDØKWX TLCA #19351 69 FJ40 "Meanie" & 1970 Boss 302 Mustang