For example you could make a power up that changes player: speed,  jump height,  fall speed etc.  

yeah, good one. I'd like to do it too :)

If implemented It would be nice to see options for increasing / decreasing by a set amount  too rather than setting it to a particular value. so you could have for example a power up  jump increases hidden across the maps that increase jump hight by small amounts each time and create stat increasing options.