Not _much_ (yes, there is something) you can do about being sumkilled if you
are not in off-mode and in general get very lucky if you happen to be a
mission. And generally you know being a mission once you get summoned and if
that is the case it's somewhat unlikely that you know it in advance to use
safeguards against summon.
... and most anti-summon things are not 100% (yes there are some, which not
everyone has etc etc.)