Magic Find doesn't affect anything in your list at all. All Magic Find does is when an item type drops, it decides if it is white, magic, rare, set, or unique. The more Magic Find you have, the higher the chances of it being more than just a white / blue. Since the special boss items / puzzle boxes etc are set to ALWAYS be unique, set, or whatever, Magic Find will not affect these. Runes are always white, so similar situation for them. Magic Find is good in just about every area except for bosses that have a specific loot table designated.

As for people discussing the player count affecting things, it can affect things that can drop from every monster (given the monster is high enough level). Meaning, player count can increase the chance you get a rune, puzzlebox, and enchantment. It will not help on boss specific uniques / sets.