so im attempting to do a guitar cake this afternoon and tomorrow, I think I might/kinda/not really have an idea how I'm going to pull this off but does anyone have any tips that might help? I'm thinking of carving the body of the guitar from cake and doing the neck out of rice crispies.

How realistic and proportional does it need to be? I've done a couple that I cut from a 9x13.

I did the neck from rice krispies, and I think it worked pretty well. Unless you make the neck really thick, though (which, in reality, it isn't), you'll have to make some supports for under the neck. I used styrofoam.