Hide the gun in your backpack

You pull out some of the cans and bottled water, double-check the safety on the PS90 (because that could end very badly otherwise), and manage to squeeze it into the backpack. It doesn't all fit. Several inches of the barrel still protrude. But the barrel, all by itself, doesn't look threatening. At a casual glance, it might be mistaken for an antenna or a tripod leg, or some other harmless piece of equipment. You practice pulling it out and putting it back in a few times.

You can draw it out fairly quickly (though still not as quickly as you could shoulder it), but putting it back in takes a minute or two of effort and rearranging every time. Of course, you figure that if you ever have reason to pull the gun out and then put it away again, you'll probably have all the time you need for that last step--because whatever threatened you enough to prompt you to draw your gun in the first place will be full of bullets at that point.

The major downside is the amount of food you had to leave behind: two day's worth. You remind yourself that it's not that far to Uncle Leroy's compound and that you'll probably be just fine.