Define Grab and bug out scenario - if its a mayor global event you should have some type of an emergency plan. If i would have to ditch everything and get out i would probably build a 308 AR - something that i can hunt with for food, nothing special Iron Sights a must, secondary choice is some kind of a scope - we all have the Red Dot sights and the EOtech's but they all run on batteries and they have a lifespan, my preffered choice 1-4 x 24 scope it gives you a close combat capabilities with some range also - i use a Nikon M 223 1-4x24 scope it is probaly best priced scope inits class that is very easy to use and it holds zero u can find them for about $ 250.00. Magpul MS2 Sling that u can use in 1 or 2 point configuration, few spare mags and some type of a minimal cleaning kit.
If a major event hits us be prepared and plan for it, number 1 thing to remeber be quick and get out - that means get out of populated areas - big cities towns, the more people you have around the more difficult it gets.