If I had one wish, it would be to be able to cast all the spells out of DnD (all editions) with all possible feats if I so chose, with no memorization limitations, as a 80th level epic caster in all caster classes, including but not limited to normal Wizard spells, Cleric, Druid, Shadowcaster, Truenamer, Psionicist, and so on.
Because then I would be a god, pretty much. Think about how horrifyingly awesome the 3rd level spell Protection from Normal Missiles would be in a gunfight. "Oh, you shoot me? All 200 of you? With tanks and artillery and planes and shit? Yeah, no effect."
Explosive weaponry? Protection from Fire/Normal Missiles and Stoneskin, as well as casting Regeneration on yourself beforehand.
And let's not get started on the fact that you have Permanency. So all this is permanent if you so choose. Not to mention that you'd be the ONLY person in the world with magic. Dimension door. Disintegrate. Polymorph. Summon Monster spells. Magic missile. Magic fucking missile would be the most OP shit ever IRL.
"Disarm him." *They do so* *You shoot them all to death with magic missile because magic*
Or Contingency. "If they shoot rocket launchers, explosive ammunition, or anything else that might actually harm me, in my general direction, I dimension door to an area at least 10 miles from anyone that could detect me." And if you Chain Contingency, Dimension door + Invisibility + Improved Stoneskin. So. Many things you could do. You'd never be late for anything. You'd always have defenses. You could charm animals at will, change into any creature, real or imagined, possible (Yes, polymorph into a fucking Xenomorph or a Predator or a Doppelganger or a DRAGON) create things at will, enchant items, or you know, CAST MOTHERFUCKING WISH. DnD magic would equal Instant Win in reality.
Sorry, might be a bit of a tangent there.