it you want a shotgun, a mossburg JIC is great because it comes with a waterpoof case and is pretty much made to be a survival gun.
>http://www.mossberg.com/product/500-jic-shotguns-51340/as far as a rifle goes, a 357 mares leg or a youth model would be good,also the ruger american compact is only 6lbs and comes in an array of calibers fro 22-250 up to .308
i prefer a handgun so i carry a Taurus judge, i usually keep 3 .45LC's in it and 2 rounds of #6 .410 for copperheads