I use a tailgate salt spreader and whatever salt is in the bed for weight. I have had 3000lbs at times, but prefer 1000lbs as any heavier is tough on truck. Its removable (80lb bags) and useable (traction).
I too have a tailgate spreader (Pro Flo 2, about 325-lbs.) riding around on the back of my truck. Once I put a few hundred pounds of salt in it, it's plenty heavy. It kind of seems like since I mounted the air bags a little to the front of the rear axle, the spreader is really good leverage for taking weight off of the front end.
Friend of mine that I use to help plow. Used concrete blocks banded to skids in the back of his pickups.
In my 2 wheel drive dump truck, my first year using it, I used about a ton of sand. Truck was pretty much unstopable. It could really stack a good pile. I had no problems moving frozen piles from weeks earlier snows that other plowers had put in the wrong place. But it was a problem for me to get rid of sand when spring came. Pit would not even allow me to just give it back to them. Finally found a concrete company to take it.
After first year and since, in the dump truck, I use a load of about 3 yards of mulch. Then, come spring I am ready to go when it is time to start mulching. I think that works pretty well for my situation. Always figured the mulch would work as a traction use if needed, have never had to find out yet, though.
In pickup, I use solar salt bags. About 10 - 15 bags depending on weight of bags, 50lbs - 80lbs. After season, I use up the salt for my house water softner.
Unfortunately, I do not do salt apps, but those that do, I think have a ideal setup since all ready having to haul salt.
We got hit with about 16 inches yesterday and i didnt have any wieght in the back of my 350 so i called a loader over and puff 2 yards of snow in the bed worked great.Now that the storms over i gotta thaw it out!