I think range bags are like boats, you want a bigger one until you get one that is too damn big.
My current is a Pelican 1500 and it is very strong and carries better at my side like a briefcase. This goes with me anytime I go to the range and has my ear pro (plugs and electronic muffs), six magazines in a pouch (that I typically load at home on the bench), staple gun, another little pelican box with loose rounds, a few Crown Royal bags for brass, and a pouch that I think I bought in a luggage department that is supposed to be a toiletries kit for travel. In it goes the timer, a Leatherman tool, squib rod, spare timer battery, basically all of the stuff that I probably will not use (somebody else always brings their timer...) that stays out of the way unless needed.
If I am just shooting pistols I typically am carrying the gun I will be shooting, if I am bringing one extra handgun it probably fits in the 1500. But there is not a lot of spare room, so if I am bringing anything much else (including if I am bringing guests) it goes in an annex bag, typically one of those cheap tool bags from Lowes/Home Depot/Harbor Freight. Or maybe I am bringing an AR, and I have a two rifle case from Midway, it works great for throwing extra pistol stuff in the second side.
I finally broke down and created a waterproof tool box that has the rifle rests, spotting scope, and chronograph in it, and it can stay in the truck or in the garage handy.
This is all an effort to minimize what I am lugging in and out of the basement with the ammo supply in it to generally just the Pelican 1500.