It's so much cake, how do I cut recipe in half?

As an alternative to Nancy's and HalfPint's suggestions, what I do when halving a recipe with an odd number of eggs ("cutting an egg in half" as it were), is beat that egg and use about half the amount. I don't weigh, just go by eye. Thus, crack the first two eggs into a bowl, crack a third egg into a small bowl, monkey dish or custard cup, beat with a fork, and pour out roughly half. (I know, the remaining half-egg, what to do with it?.....I'd probably scramble it up with an extra egg or two later for lunch).

I was going to suggest two methods.
HalfPint has given one.
The other is to make the full recipe cake and full recipe frosting, but only frost & eat one of the two layers
Freeze, separately, the remaining layer and half the frosting for a future date.

Since the 5 eggs are for the cake, beat all 5 together and use half (volume or weight) for the cake and save the other half for breakfast (scramble?) or another use.