Dirt Be Gone.
Nothing will ruin a hunting trip quicker than looking through your scope to line up that once-in-a-blue-moon-oh-so-perfect shot and seeing not your target, but a 4-power, coated optics-enhanced smudge. A blob of grease from a finger, maybe last night's chili, dust from the trail or water droplets from the morning mist. In a panic you might try to clean it off with a shirt sleeve, some spit, a handkerchief or even that same greasy finger that made the mess in the first place. Don't! You need to clean that scope properly or risk damaging lenses and coatings.
The Pen Is Mightier Than The Dirt
In an earlier post I mentioned a product from Cabela's called the LensPen (note, Cabela's and I have no relationship, other than when I send them large sums of money, they send me small boxes containing goodies) For about $10, you get a pen-like device, about the size and shape of a Sharpie pen. One end of the the LensPen holds a retractable brush, something like a makeup brush that your wife or mother might use to put on whatever that make-up stuff is they put on (pay attention). At the other end, removing a cap reveals a felt-like pad (chamois, I'm told) impregnated with some sort of non-liquid cleaner.
The proper use of the LensPen is pretty self-explanatory. You first use the brush end to remove visible dust and grit from the optics. Combined with gently blowing off larger particles of gunk-n-junk (my technical term), the brush makes a good first stab at getting your lenses cleaned up.
The other end, what I call the 'swab' end, is then used to get things like grease, oil and condensation off the lens. Since this means you will be rubbing the lenses to remove contaminants, you have to be careful here. If you leave fine grit, dust, dirt or other abrasive detritus on the scope's objective or eyepiece, the pad-end of the LensPen will grind some of that junk right into your lenses like ultra-fine sandpaper. That translates into lots of fine scratches in your field of view. If the scratches are bad enough, you will compromise the functionality of your scope. Some scope manufacturers can replace or polish & recoat lenses, but that won't do you much good 7000 feet up on the side of a mountain, staring down that trophy bear or deer. Be sure to use the LensPen's tools in the proper order and fashion and that dirty scope will quickly become a clean scope, ready to help you put that perfect shot downrange. Bear in mind that this tool is equally effective at cleaning binoculars, range finders, and spotting scopes. It's versatility far outweighs its cost.
Cover That Thing
The next item is what I call a preventative measure. Since I use exclusively Leupold scopes for now (again, no business relationship here, other than whenever I send a Leupold dealer large sums of money, they ship me back a small box with a pretty trinket inside), I also use their line of Alumina flip-back lens covers. These covers thread into the objective and eyepiece bells of most 2005-and-later Leupold scopes and feature spring-loaded covers held shut with a strong magnet. A firm push on the exposed tab on the objective's cover piece causes it to flip up and out of the way. On the eyepiece covers, Leupold installed a thumb release that causes the cover piece to flip up and out of the way as you push the release forward. These work incredibly well for right-handed shooters because as you shoulder your rifle or shotgun, your left hand's thumb will be close to the exposed tab on the objective cover. A quick flick of the thumb and that cover is open without adding any awkward motion to your shouldering sequence. On the eyepiece end, as you wrap your right hand around the stock and trigger guard, your right thumb will come relatively close to the thumb release for the eyepiece cover. Again, a quick press of the thumb release and the eyepiece cover is open for business without any interference to your normal shouldering motion.
These covers are not cheap (expect to pay about $35-$40 each), but they do a good job protecting your scope lenses from dirt and contaminants as you hike through the terrain. They are also easier to open than "bikini" style scope covers during that adrenaline rush of seeing your target. The flip-up covers get out of the way and stay out of the way. There is nothing to fall off, nothing to fumble with and nothing to worry about losing or stowing in a pocket. When a shot presents itself, you have better things to worry about than what to do with your scope cover.
On The Cheap
For the hunter on a budget, there are other flip-up covers from other manufacturers, i.e. Butler Creek, that may fit the bill at a fraction of the cost. I do not have any experience with Butler Creek's lens covers, but they may be worth a look. I have some of their other products and have always found their products to be of decent quality and workmanship.
The budget-minded may be able to get away without spending the money on a LensPen. Many women's makeup brushes are made of natural, non-abrasive fibers and will fit the bill nicely as the 'brush' end of a LensPen. I'm not sure what goes into makeup, but it always looks powdery to me. Powder means grit and grit means scratches. So, get your wife/mother/sister to give you a new, unused brush. I'm pretty sure makeup brushes and rabbits share some common genes, as both seem to multiply exponentially. These brushes are often given out as freebies to the ladies, so this is cheaper than cheap - it's free.
As for the other end of the LensPen, odds are if you bought a scope or a set of binoculars, it came with a soft cleaning cloth. This will do in a pinch for getting grease, oil, and moisture off your lenses. Keep this and your brush in your shirt pocket and you'll be ready to keep those optics clean and at the ready. As an added benefit, if you wear glasses, you can keep those clean with these same tools.
Keep those scopes clean and at the ready for when you need them most.