It is actually a planned feature to have something like this by the first beta, but if you know enough actionscript to think you could implement it yourself, the inventory is stored in an array on the main timeline called 'keysOwned'
each key (though it could just as easily be an item) is stored as a string in this array.
Like I say it's a feature I plan to implement to some degree anyway, but I can't say when it will be done (I'm not a reliable dev sorry ^_^;) so if you want to do it yourself the 'keysOwned' array is where you want your code to look at for the inventory
