My flying is a little different. We do a lot of auto parts, so I get a few big containers on skids, large boxes, large plastic cartons, etc. The sizes vary, but a common size is 4x4x(height varies) feet.
When I pick up the paperwork at dispatch for the trip, they'll have the number of skids or packages, the dimensions of each (unless it's a "loose-load" run like MikeD described above), and the weight of each (or total estimated weight in the case of a loose load).
If it's a heavy load, I check before takeoff to make sure that I'm not going to be overweight (the dispatcher also checks when they book the trip, but I doublecheck). That way if need be, they can de-fuel me as necessary. The Caravan can carry roughly 2400 lbs. of freight (give or take a little depending on the airplane), WITH full fuel (2200 lbs.). Unlike some airplanes, fuel burn does not affect the CG very much. It only moves very slightly forward as fuel is burned, which puts it more towards the center anyways.
Once I make sure I'm all set with fuel weight (that I have enough AND that I'll be underweight), I blast off to go get the freight. Once you've done this a few times, you pretty much can do the "balance" portion in your head for simple loads like a medium weight skid or two. If it's small, super heavy boxes, awkward sizes/weights, etc. (basically anything unusual), I still do a full W&B sheet because there are limits to how much weight you can put in each zone, and also limits on floor loading (lbs. per square foot). This I normally do enroute to the pickup point, or if I'm early, at the pickup point while I wait for the freight to arrive.
Loading these big skids is the hardest part, since the heavy ones have to be moved forward in the plane. I'll put the tailstand in, then guide the forklift into the door. Before they let down the skid, I put a couple of thin plastic "skis" under it so it will slide easier on the waxed wooden floor. If it's a plastic container, I skip that part, since they slide easy anyways.
If it is a plastic container under about 1000 lbs., I can usually muscle it forward myself. If it's a wooden pallet over about 900 lbs., I either use a crank (think manual winch), or a come-along, both of which are a slow pain in the ass process. Or, I demand the line guy get his ass up there and help me push ( j/k
). Loading it is harder than unloading. The floor in the Caravan slants downward slightly from front to back, making unloading a little easier.