White Box Innovation

Filling In The Gaps
"What do you want to do?" the referee asks. The answer is often something not covered by the rules found in the LBBs. Sometimes, maybe most of the time, no rules are necessary because the player's response involves no risk to their character and little chance of anything unusual happening. Often roleplaying a conversation or two makes everything clear, such as discovering information, or haggling for a price. White Box being a game of imagination invites the players to be inventive, and they will often come up with unexpected responses, unusual approaches and innovative solutions to situations described by the referee. Some of the proposed actions involve risk and an in-game mechanic seems to be the way to resolve the outcome.
The referee says, "Your way ahead is blocked by a deep fissure, the sides are steep and slippery.  There is an old plank placed across the fissure, but it looks mossy and deteriorated. There are some roots showing through the crumbling ceiling above the fissure. What do you want to do?"
After asking a couple questions and finding out the bottom of the fissure is "out of sight" deep and the width is some 10' the players may decide to try swinging on a dangling root, jumping across or walking the plank (or any number of other creative solutions). The referee may decide all are risky behavior that might result in a fall, none are really covered by specific rule mechanics.
In the above situation an innovative referee will probably go outside the rules as written and ask the players to make dice rolls to determine success.  This can be a simple random roll on say a d6 with a chance of success based on the referee's judgement of the difficulty of the task..."Roll me a d6 and don't roll a one." Alternatively if the referee (perhaps influenced by player argument) decides some skill/attribute may be involved they can call for a die roll based on that skill/attribute. White Box PCs have six attributes which indicate the character's relative abilities in various spheres of activity. Perhaps a dexterity roll is called for.  If the referee likes the idea of using the bell curve percentages, three d6s may be rolled and compared to the PC's dexterity score. Alternatively a d20 can be rolled and compared to the dexterity score. Situational modifiers can be used as the referee sees fit.
In my own game I like to let players assign backgrounds to their characters, often at char-gen, but sometimes during early play. The PC background can be just about anything and as specific or general as they like. I then encourage them during play to argue that their background would help their PC in doing certain tasks, which if I am in agreement, gives them a bonus to succeed.
This is just a small discourse on innovation limited to just one aspect of game play, but it hopefully begins to illustrate the possibilities of adding to the rules as written. For me it comes down to preference. I would rather make something up and see how it works than look up the rule and take several minutes away from the game to do so. In life and play, timing is everything and keeping the game flowing is very important at my table.