It seems like EK clarified that, if you have access to EK.
Some that come to mind that you should know IMO: speed of light, R (as in pv=nrt), avogadro, speed of sound = 343, a general idea of wavelengths and frequencies of visible light and sound, gravity = 10ish, 1atm=760mmHg=760torr, stp, standard conditions, specific heat of water, density of water, 273k=0c=30f, that's all I can think of right now. Other people might add to the list.
TPR suggests knowing Coulomb's constant, which is 9.0 x 10^9. Density of water. Not really constants, but I've found it really helpful to memorise sine and cosine values for 0, 30, 45, 60, 90, and 180 degrees.