One of the most arduous parts of Marine Corps life and training has to be the long-distance rucks. Covering a lot of miles with a lot of weight on your back may seem like a simple enough proposition, but as time goes by, you start to pick up on a few things that can make an otherwise grueling hike just a bit more pleasant--or at least, a bit less likely to cause you the sort of nuisance injuries that can really make a week in the field feel more like a week in hell.
While the nuts and bolts of a long distance hike are simple enough (bring adequate food, water, and appropriate emergency gear, then just put one foot in front of the other until you're finished) there are some things you can do before you set out or carry with you on the hike that will pay dividends throughout the hump and after, as your body recovers.
Use dry deodorant to manage chafing
Despite how much I've worked out throughout my adult life, I somehow never quite managed to get one of those "thigh gaps" all the girls on Instagram keep talking about, and as such, chafing in my groin and between my thighs has always been a concern on long-distance hikes. The combination of sweat, the seams of my pants, and my rubbing thunder thighs always conspire to leave my undercarriage raw, which quickly becomes a constant source of pain as I log the miles.
Even with spandex undergarments and an industrial supply of baby powder, chafing can rear its head and ruin your day, but you can relieve a lot of that heartache (or, I suppose, crotch-ache) by rubbing your dry stick deodorant all over the affected area. The deodorant creates a water-resistant barrier that protects the raw skin as you keep on trucking. This trick has worked for me in the savannas of Africa, the busy streets of Rome, and even in the relentlessly humid Georgia woods. Remember--it's got to be dry stick deodorant. Gel stuff just won't do the trick.
Carry a sharpie to keep tabs on bites
Spider and other insect bites can be a real cause for concern on the trail, and not necessarily for the reasons you think. It's not all that likely that you'll get bitten by a spider with the sort of venomous punch to really make you ill, but even an otherwise innocuous spider or insect bite can turn into big problems in a field environment. Bites create a high risk for infection, and not everyone responds to exposure to venoms, bacteria, or stingers in the same way. That's why it's imperative that you keep an eye on any questionable bites you accumulate along your hike.
Use a sharpie to draw a circle around the outside perimeter of a bite when you notice it, then note the time and day. As you go about your hike, check on the bite sporadically to see if the swollen, red area is expanding beyond the original perimeter. Add circles with times as you check if the bite continues to grow. If the bite grows quickly beyond that first drawn perimeter, is bright or dark red, and feels warm and firm to the touch, seek medical care for what may be a nasty infection. If you experience any trouble breathing, that's a strong sign that you may be going into anaphylactic shock due to an allergy, and you need immediate medical care.
Add moleskin to blister prone spots on your feet before blisters form
If you've done any hiking, you're already familiar with moleskin as a go-to blister treatment, but most people don't realize how handy moleskin can be for blister prevention as well.
If you know that you tend to get blisters on certain spots on your feet during long hikes (the back of the heel and the inside of the ball of the foot are two common hot spots, for instance) don't wait for a blister to form to use your moleskin. Instead, cut off a piece and apply it to the trouble spots on your feet ahead of time, adding a protective buffer between the friction points of your boot and your feet themselves.
It helps to replace the moleskin about as often as you replace your socks, to prevent it from peeling off and bunching up on you (causing a different hiking annoyance), but when done properly, you can escape even the longest hikes pretty blister free.