I read a book once by Roger Zelazny called Creatures of Light and Darkness. There was an agnostic prayer which might work too:
Insofar as I may be heard by anything, which may or may not care what I say, I ask, if it matters, that you be forgiven for anything you may have done or failed to do which requires forgiveness. Conversely, if not forgiveness but something else may be required to insure any possible benefit for which you may be eligible after the destruction of your body, I ask that this, whatever it may be, be granted or withheld, as the case may be, in such a manner as to insure your receiving said benefit. I ask this in my capacity as your elected intermediary between yourself and that which may not be yourself, but which may have an interest in the matter of your receiving as much as it is possible for you to receive of this thing, and which may in some way be influenced by this ceremony. Amen
I was once discussing religion with some friends, one of whom claimed to be agnostic. The agnostic one was advised that, when you die you will see a light and should go toward it. He was further advised that if the light is flickering to turn around and run as fast as possible in the other direction.