Impeccable Planning

With foresight and preparation, you always have on hand what you need to succeed. A number of times per session equal to your Knowledge skill, you are able to retroactively declare you have just the sort of item prepared for the challenge in front of you. Examples include having a backup weapon, or spare rations in case you get lost, or a map of an area, or you've managed to bribe a guard into giving you a key to the area you need to get into, or you had anticipated you might be facing a particular monster and happen to have its one weakness with you. 
If you have prepared spells such as an alchemist or rune marker might do, you can also retroactively switch out which spells you had prepared, each time counting against your daily limit.