Resupply
To me, what makes a hike 'long distance' is that it's impractical to do it without acquiring additional food and perhaps equipment along the way. True, one could walk 150 miles in a week with all the necessary food. And that's quite a hike. However, if you have the skills and conditioning to do that, the only change you need to make to walk all the way across the country is to get some more food once a week and keep on going. So how is that done?
Your options are: buy in each town, mail it from home, buy it in big towns and mail it ahead, cache it, or find it along the way. Most hikers use some combination of these options. Each has its advantages.
Buying
I try to buy my food in each town. It's easier. I don't have to guess 6 months in advance how hungry I'll be or whether I'll want to eat yet more dried apricots. No one at home has to visit the post office once a week. I never miss packages that got lost or are locked up until Monday. The food in town might be a bit more expensive, but I don't pay to mail it. On the bad side, the small stores may not stock much. And some food in little visited stores may go stale.
Mailing from Home
US Post offices can receive mail for people who don't have local addresses. This is called General Delivery. Someone mails a package to:
Dan Bedore
PCT Hiker
General Delivery
Rivertown, CA 91234
Estimated Pickup June 10, 2016
The hiker needs his ID card (so a trail name is never used in the package) and claims the package at the post office retail counter.
Post Offices close to popular trails handle this regularly. On little traveled routes, it would be wise to call ahead and discuss general delivery with the local postmaster. If not picked up, the packages are eventually returned. But for some post offices, this happens after a few days, and for others, not for months. The hiker needs to make sure the package will still be there when they arrive in town.
Usually the hiker buys all of his food in bulk, selecting exactly what he wants, and thereby saving money. For each post office where the hiker plans to receive supplies, a box is prepared and addressed. Each box is left open. The hiker calls home a week or two in advance. Adjustments can be made, like adding a pair of socks or some medicine, or tossing out some crackers the hiker is sick of. The box is mailed and arrives before the hiker.
A variation on this is ordering food or equipment and having it shipped to some point along a trail. Many hikers have had boots, tents, or etcetera, fall apart near some small town with no gear retailer, and have done this.
Another variation is to mail the packages to businesses along the way. Most charge for receiving packages.
Bouncing
Some hikers prefer to mail one sturdy container from town to town. Say a hiker wants to use a computer, shaver, battery charger etcetera, in a hotel in each town, but does not want them out on the trail. They get into town on Wednesday, pick up the bucket at the post office, use its contents in the hotel that night, and on Thursday put the stuff back in the bucket and mail it to the next town before hiking out. Now they can use a computer on the trip without carrying it on their backs. They can also buy extra food in large towns and pick it up where tiny stores might have only candy and potato chips. They can leave extra socks in the bounce box until the ones they're wearing get holes.
Caching
Caching food for a six month hike across the US might not work because animals, weather, or other people might get to it before you. Also, caching is illegal in some places. Still, it might be a great option for a two week hike where only one cache in the middle is required. Maybe before the hike you would drive to the middle, go off in the woods, and bury or hang the cache out of sight. Now you don't have to spend the time and money hitching into town and resupplying. If you leave the container or trash at the cache site, you'll have to go back and retrieve it. But if you plan it near a public trashcan, you might resolve the issue that way. Of course, if you cache food, and don't go to town, you won't get showers, laundry, restaurant meals, and everything else that towns offer.
Wild Food
Some food grows out in the woods. Onions, mint, berries, and more are easy enough to find and identify in season. They add flavor and vitamins that are missing in packaged foods that hikers often carry. And it's a lot of fun to find them. Bradford Angeir's book Field Guide to Edible Wild Plants has great illustrations and descriptions of wild plants with which you can supplement your diet.
Hiker Boxes
Hiker boxes are another source of free food and equipment. Often post offices, hostels, shelters, and other places frequented by hikers have a box in which hikers drop off excess useable food or gear. Other hikers pick up whatever they want or need. On heavily traveled trails like the AT and PCT, hiker boxes are a great resource.
A Typical Resupply Trip
Some hikers love to spend a lot of time in town, taking zero days to rest, or socializing, or who knows what else. I find time in towns a bit stressful, what with worrying about what I can't buy but should, etcetera. So I try to get in and out quickly. Hotels are usually where I shower and launder, so I typically stay one night. But after so many quiet nights in the woods, I find it tough to sleep in hotels, what with people walking around, slamming doors, keeping the TV or conversation loud, etcetera. Unless there are other hikers to socialize with, I usually try to get in and out of towns as quickly as possible.
Groceries
There are 4 categories of grocery items I need in towns. One is batteries, aspirin, and other expendable non food items, which I replace as required. Two is town food, fruits and vegetables, dairy, and perhaps cooking supplies if a kitchen is available. I want to eat all the nutritious foods not available on trail when I'm in town. Three is food that will last just a few days in a pack. Fried chicken, carrots, fruit, whole grain bread and cheese are examples. The fourth category is foods that last a long time in the pack. For each day there might be granola, mashed potatos, nuts, sausage, raisins and dried bananas.
Returning to the Trail
The next day, once all the chores are done, I can hitch back to the trail early, or hang out to socialize, use the library or internet, or beat bad weather.