I was reminded by this post by Joseph Mason about my Luck house rules. I'm sure I posted these before on numerous mailing lists and forums, but here they are again. If only for the edification of my new players (who run Bern and Galoob) in my Felltower game.
Luck: Luck is by-the-book, except in combat. Each combat is treated as one hour of time, regardless of actual elapsed time (in game or in the real world). Therefore, Luck allows you one re-roll per combat, Extraordinary Luck two re-rolls, and Ridiculous Luck six re-rolls. The time between uses doesn't matter - you can use your Luck on consecutive rolls if you wish - Luck comes in streaks in combat!
Once Luck is used in a fight, you cannot re-use it until the fight ends and the appropriate time interval has passed. For example: Bern uses Luck at 4:38 pm in a fight. If the fight ends at 4:45, he may use Luck again at 5:38 pm or later. If the fight is still going at 5:38, he has to wait until it's finished.
Exceptions will be made for exceptionally long fights, such as multi-session battles. In such cases Luck will usually reset between sessions - but it's at the GM's discretion.
That's how I've run Luck for a long time, especially since my previous campaign featured a number of PCs with Luck and a lot of very awesomely long fights (like the three-session fight against Lurg No-Teeth, Orc Boss) and end-of-session battle starts. It also nicely discouraged people from stalling in combat to get their luck back - not that people did it, but why even have such a temptation on the table?
We've used this rule for so long I think we sometimes forget to tell anyone, because the assumption is it's practically the rule as written.