What rules would you put into your OSR stew?

Following up on my article on innovation, there was some intriguing discussion related to the subtle difference between creativity and innovation, which got me thinking...

If you were to make a giant OSR gumbo, what ingredients from different games would you stir together? 

• Encumbrance from Lamentations of the Flame Princess? 

• Kingdom management from Adventurer, Conqueror, King?

• Initiative and combat movement from HackMaster? 

• Prime attributes from Castles & Crusades? 

• A crap-load of spells from Fantastic Heroes & Witchery?

I'm curious to know more about what the community believes are the coolest or most interesting rules or mechanics that OSR games have added into the mix.

Name a mechanic and let me know why you think it's cool enough to stir into the stew. I'm interested in what kind of beast might emerge from the conglomeration.