I have never messed with adding weight, and in general have never had much of an issue. I've found that for the most part good tires and the weight of the snow that landed in my open bed have been enough. But I also have been driving my Ranger from my first day behind the wheel, and learned winter driving in it. If you are used to something else with a different balance there is a learning curve.
Most cars and SUVs have more weight over the rear axle due to body mass and fuel tank position. Rangers in particular have a very light bed, and most pickups (Rangers included) have the fuel tank in front of the rear axle. when you have a long vehicle like this and 90% of the vehicle's mass forward of the driving axle it makes the vehicle longitudinally unstable and it can be easy to put the vehicle into a spin. There is a particular corner near my house where I have spun my Ranger several times over the years, not even in snow, just in rain.
Two to three hundred pounds seems to be the preferred weight point, but more could be added. Being a 1/4 ton pickup 500 lbs (minus your own weight) would be your max legal limit in most cases. But nobody pulls Rangers over onto a scale for a weight check.
Positioning the weight right over the rear axle will get you the best results, so you would want to find a way to keep it between the wheel wells in the bed.
Weight is weight, so anything that gets the desired pounds will do, some people prefer sand bags because if you get yourself genuinely stuck you can use one (or more) to perform a ritual sacrifice to the traction gods by spreading its insides around your wheels and they may bless your tires with enough grip to get out on your own. But I also keep tow straps in the cars just in case.
Leave your spare tire in place, think of it as "free weight" since it was calculated into the truck's curb weight, and doesn't count against your legal limit. Heck, I'd probably take it down and fill it with RV antifreeze or something, then put it back up.