I have this one from Midway:
The MidwayUSA Competition Range Bag was built from the ground up to be the best range bag on the market. Perfect for competition or a day at the range,...
www.midwayusa.com
I love it. It's very rugged with strong zippers. The top/main compartment has a double zipper pull that opens quickly and gives you a wide mouth to drop in ammo boxes, spotting scopes, pistols, or other big items. There's one full-length and two half-length side pockets - I can't tell from the current photos if they've changed it (they don't show the smaller pockets opened up) but mine have AR-style mag pockets on one side and pistol on the other. And there are smaller pockets on the ends that are just right for eyes+ears, small items/tools, and a dedicated water bottle pocket. The whole thing sheds water pretty well, and so far I've had it nearly 3 years with no sign of wear.
I keep mine "ready to go" at all times. I always have a useful mix of shells and cartridges on hand anyway, so this is one less "bugout" item I need to think about.
Edit: Looks like they now have two basically identical bags, one specifically for AR and one for pistol. IMO the AR mag pockets are a little clumsy - I think flaps and velcro aren't super useful INSIDE a bag - they just hinder access. I prefer the pistol style... but YMMV.