RV antifreeze, windshield wiper fluid, calcium chloride solution, beet juice (rimguard), and probably maple syrup or anything else that won't freeze where you live. So probably Jack Daniels too.
Both my tractor's tires are filled with calcium. Good to go down to minus 40 degrees.
Never a single problem,exept for a leaking valve corroding the rim.
All those tires have a inner tube.
In my opinionm ballast is a must for serious tractor work. Traction and balance beeing part of the equation.
Methanol aka Methyl Alcohol is also a common fill. Usually mixed with water to some degree. Methanol is the active anti-freeze ingredient in Windshield Washer Fluid.