Sorting cases for reloading is one thing...( and yes its a pain in the butt )...and the only way to do it with any success, in my view, is after you clean them...to stand them up on a flat loading table...and segregate as you sort them / but yes, even that is hard.
....having multiple calibers of ammo on the bench at the same time is another issue ( sure its easy to mix up a .380, or Makarov or 9mm...) that's why, in my view, having a few boxes of each on the firing line bench at the same time is a mistake / because they're so close in size and easy to make a mistake...
I can see breaking the rule if you have a 9mm and a .357 Mag at the range...(its not too hard to easily see a 9mm vs a .357 Mag on the bench....so mixing them on the firing line bench is not such a big deal ..).../ I often go to the range with more than one gun..and more than one caliber too / but its not that big a deal to keep the bench organized using a small zippered range bag for ammo. Just food for thought...