Please see here for Planck units:
http://en.wikipedia.org/wiki/Planck_units
Even though most of these are outside the range of our everyday needs, they have the advantage of being truly universal constants, they are the same everywhere in the universe.
So, I suggest to include
Planck mass m_P = 2.17645E-8 kg on the "mass and weight" page,
Planck length l_P = 1.61624E-35 m on the "distance and length" page,
Planck volume l_P³ = 4.22199E-105m³ on the "capacity and volume" page,
Planck area l_P² = 2.61223E-70 m² on the "area" page,
lightspeed is on the "speed" page anyway (good!)
Planck temperature T_P = 1.41679E+32 K on the "temperature" page,
Planck time t_P = 5.39121E-44 s on the "time" page,
Planck pressure p_P = 4.63309E+113 Pa on the "pressure" page,
Planck energy E_P = 1.9561E+9 J on the "energy and work" page,
Planck power P_P = 3.62831E+52 W on the "power" page,
Planck torque M_P = 1.95609E+9 Nm on the "torque" page,
One could even construe a "Planck fuel consumption", which would be a relation between the fuel consumed (in units of Planck volume) and the distance travelled (in units of Planck length). I guess that would get you to the limits of internal floating-point math :)
Have a good work! toby