I get the feeling that optimal short term cognitive enhancement is going to have a price. My vision on that is that it's going to be a short "crunch" time.
Think about first providing the optimal environment for the brain...brains love glucose. There is no way around this. Ketones aren't going to do it for the short term, though they might serve just fine for the long view. The trick is to get a very functional level of glucose entering the brain during that period. The paleo complex carb sources people like would be fine, I'd imagine.
A multi-factorial stimulant package would also be needed. A suite of several complementary smart drugs come to mind coupled with a mild amphetamine like ritalin or maybe another ADD drug. I'm out of the smart drug game, and have been for a few years, but a quick browsing of relevant websites should reveal what's good. As far as supplements: Acetyl-L-Carnitine, L-tyrosine, gingko biloba, DMAE, phosphadyl serine, maybe even L-taurine.
I don't even know where to start with the smart drugs, but selegine (deprenyl), piracetem, and vasopressin might all be candidates. I know there are some updated version of these available nowadays.