So many ideas.
Is this a one-item, one-time thing?
Shame.
Scorpion? Tempting.
Lifestone? VERY tempting. Only problem is that some sod would figure it out and then your tied resurrection location would become the most valuable ten-foot-square piece of real estate in the world.
How about that priestess in the G-string, thigh-high boots and cloak from the Temple of Akatosh in Daggerfall? You know the one, nice figure, never stops dancing, can cure any disease instantly and does it for free a few days of every year. Malaria, HIV, sleeping sickness, dengue fever, hepatitis A, B and C, yellow fever, rabies and Japanese type B encephalitis can all **** off.
Well, maybe not. Hard to cure all the wild animals. She'd certainly help, though, and the Taliban couldn't do a thing about her costume. Non-roving NPCs in Daggerfall were utterly indestructible.
How about a Mamba or Adder or the Transporter from Elite? Yeah, the Cobra III's the superior ship but it can't land planetside so you'd be out of luck right away, wouldn't you? With the Transporter you can take David Attenborough and Patrick Moore on a tour of the spiral arm and land almost anywhere.
If it has to be a summoned thing, a Daedric Dagger from Morrowind has its advantages. Mugger? *zap*shlorp* Investigating officer? "Show me the murder weapon." It could have been very useful on board flight 97.
I think I have one to trump those, though. Angband: magical figurine of an Archangel. You throw it into a room, not at a creature, and it turns into an Archangel on your side. Among the things an Archangel can do is summon an angel, which could be an Archon, Seraph, Archangel or Cherub, also on your side. Archons and Seraphs also get this ability, and the Cherub gets to summon friendly monsters. Luckily, none of these things ever needs to eat (unless the Cherub summons a green worm mass, in which case you need a wand of wall building with a lot of charges fast) and they only summon when they see an enemy.