Whether you live in an area unfriendly to firearms or simply don't wish to tip off your nosy neighbor to your 2A proclivities, being able to discreetly transport a carbine helps keep unwanted intrusions to a minimum. While it shouldn't matter what you're transporting, there are a number of reasons why we might want to keep things under the radar.
In that vein, the Colt-branded Bulldog Cases MSR Sling Pack is one such choice. Built to transport a carbine-size AR-15-style rifle. It accomplishes this in one of two ways: the carbine can either be broken down into upper and lower receivers and stored in separate padded sections, or it can be collapsed, intact, with a zip-out, covered area for the barrel. It might look a little odd, but offers enough concealment to keep the busybodies away.
There's a detachable fanny pack for carrying smaller items that also allows a pistol to be carried discreetly yet available if needed. A mesh area ideal for a water bottle sits on the straight edge, and the front of the pack has a high-visibility interior pouch for small items you need to spot immediately.