While I've not used real coal for hopper loads, I have used real coke. The stuff that I used is called coke breeze, and it's the "fines" from coke-making. It's not too heavy, but is quite dirty, with lots of dust. I sifted mine to get only the smaller particles, although real coal is shipped in several different sizes, depending on its intended use. I'm currently using it in my steam loco tenders, but some also moves in hoppers. I probably have enough of it to do only one 12 car train, though.
By using it loose in the bunkers, it's easy to depict a loco either at the start of its run, or later in the journey, when part or most of the load has been used up.
I also use some of it in hoppers, particularily if they're going to be spotted at the coaling tower:
Here's an aerial view of coke breeze in a hopper.
This car, also partially visible in the previous photo, is loaded with locomotive traction grit, used in place of sand for the locomotives at the steel plant where I used to work. It is quite dust-free, although some of the particles are slightly magnetic. It is also quite dense: this loaded Athearn 34' hopper weighs 8 ounces. The shiny quality of this material simulates Athracite better than the coke breeze, but, as far as I know, this is the only size available. I have enough of this stuff for several trains.
All of the loads shown are loose, and haven't caused any problems, although a loaded coal train will need adequate power to move it over the division. Your trackwork should be decent, (a good idea for any trains )

your rolling stock in good repair, and your operating speeds prototypical. The last spill occurred when my grandson was running a train: the loco and tender, running light, went through a switch lined the wrong way, and both ended up on their sides in a field, dumping coke breeze onto the scenic ground cover. I used a soft 1" brush to sweep most of the spillage onto a sheet of paper, for re-use. The rest was left at the scene, although I'll probably vacuum it up next time I'm vacuuming the layout room. The switchman responsible for the derailment shall remain nameless.

ops:
When loading hoppers, I do it either with the cars in the staging yard, or individually, in my hand. I use a paper cup, as it's easy to form a pouring spout by squeezing the cup. To empty the cars, I just pick 'em up and dump the load back into the proper container. In my opinion, the main drawback of one-piece removeable loads is that they eventually become dusty (household dust) and then look less-than-convincing.
In the photo below, the stuff in the truck is traction grit (loose), while the pile partially visible at left is the same stuff, glued in place.
Wayne