For pressure, any unit can be used

For pressure, any unit can be used. Though it's most common to see kilopascals (kPa) or atmospheres (atm), there's no reason you couldn't use bar, torr, or psi.

For volume, again, any unit can be used. Because we scientists are fond of the metric system, we prefer metric units like milliliters (mL) or liters (L). However, if we wanted to use cups, teaspoons, or hogsheads, we could do that too.

Temperature is the big one you can't mess with. You can use Kelvin (K), or, well... you really have to use Kelvin. There's no way around it, and even using degrees Celsius doesn't cut it - you've got to add 273 to your temperature in degrees Celsius to make the equation work.