Staying up all night

[MagiNinjA]

Whatever gives the most.

Also saving your turns.

[Harry Dresden]

Optimal sugar/caffeine usage is somewhat covered in this thread.

Loosely.

[TheK3vin]

Optimal is subjective, for the most part. For instance, farmers don't use Brays every day because the amount they cost is much more than their chips per turn multiplied by the number of turns they give. Personally I just used Stroopwafelen and Mister Teas, as do many people who don't like spending a lot of money for caffeine/sugar.