Rifles, part 1.

Rifles are excellent weapons for an outbreak.  They're hefty enough to give an enemy a solid whack, but not so heavy that you can't backpack with them.  They have excellent sights, even iron sights, compared to almost any other firearm class.  There are all sorts of rifle attachments on the market, from bayonets to reflex sights, and while they are amazing at long range, rifles can still be used close to an enemy with devastating effect.
  Now, let's move on to camouflage.  If you don't know where you're going (this is bad, but sometimes unavoidable), pick something that fits in everywhere, like grey or brown.  Digital camo works better than solid colors: it makes us think that what we're looking at is background, not worth noticing, and generally the visual equivalent of "white noise."  If you do know where you're going, keep some camouflage sleeves with you just in case.
  You should also get your rifle an accessory rail onto which you can mount a scope.  Then buy a scope.  These aren't just for scoring head shots; they're for scouting an area.  Of the rails you could buy, a Picatinny rail is the best.  Most rail attachments are made to fit it, as was intended in its design.  The better your sights, the further away you can be when attacking infected and the better your chances of surviving the encounter.