I like hiking in Lapland, for extended periods (6 weeks), alone
in the wilderness. The amount of stuff I can carry with me is quite limited,
and I have reduced it to a practical minimum. Here is a list of the kind of
stuff I carry with me in my backpack on a summer hike. I've never weighed
my backpack (I don't really want to know), but it's just heavy enough at
the beginning of the hike.
This list is not meant to be complete, and it must be adjusted according to where and when you are hiking, and under what conditions.
A Leatherman Wave or similar multi-tool weighs approximately a quarter of a kilogram. Needless to say, I've never carried one into the wild. As a knife it's just not as good as a real sheath knife, and in the wilderness I've never found myself needing the multitude of tools it contains. Ditto for a do-it-all Swiss Army Knife. Keep one handy when bicycling around the neighborhood, when readying a hybrid rocket for launch, or when installing a new TV antenna at your cottage, but save weight when hiking—leave the Leatherman at home. It's an urban tool.
I do not carry a GPS-unit. A GPS would only tell me where I am.
I need to know where to go, and a compass will
point me there. Once I get there, then I'll know where I am.
(Besides, a good lot of help the GPS will be once its batteries die.)
Pro tip: Copy or print your maps onto separate A4-size paper sheets. Store them in your backpack, and keep just two immediately relevant sheets handy. Place them back-to-back and seal them in a 2-liter Minigrip/Ziploc bag to protect them from the rain. The white label areas on the bags can be cleared up by wiping with acetone! I re-use my maps by writing a journal on the blank back side. Otherwise they could just as well be two-sided prints. I print my maps from pikakartta.fi. Yes, you can also get 1:50 000 maps from there.
An axe would sometimes be useful, but I've deemed it unnecessarily heavy. I've always managed to make a campfire even without an axe. Branches can be pulled off fallen dead trees, stumps are easy to kick and pull out of the ground, and dead birch breaks apart in your hands.
The Mylar "space blanket" is a generously sized, aluminized sheet of incredibly thin and tough plastic material. These are generally sold to protect against hypothermia. I have never used one for that purpose, and probably never will (I hope). I carry one because it weighs absolutely nothing, and (at least while it's unused) it is completely waterproof. So it will fix a broken tent or a leaking lean-to, and maybe if I encounter a river too deep to wade across, I'll wrap my backpack in it, and float it while swimming across the river.
The cell phone remains switched off most of the time, as there's no way to charge it out there. (Nor could I charge a GPS when its batteries wore out.) I just check text messages once or twice a week. I used to lug a Canon EOS 5D or an EOS 3 with an L-series lens, but have since come to my senses and bought a used Canon PowerShot A720 IS specifically for hiking. One of these days I might bring an amateur radio transceiver with me.
For two people, replace the one-person tent with a Hilleberg Nallo 3GT (luxuriously roomy accommodation for two!) and take along some deodorant, a standard Trangia 25 camp stove (with gas burner) and two plastic plates. Even with the Trangia stove, the pakki is most useful for cooking over a fire (e.g. when making evening tea), so I take that along as well. For the Trangia, I find that a 450 g (net) gas cylinder is just enough fuel for a week, provided you don't boil a full pot of water to make tea with every meal. If you never make tea on the Trangia, a single cylinder will last much longer. Gas is very convenient for cooking, but combining leftover gas into a single cylinder is a bit more tedious than pouring spirit from one bottle to another.
Carrying all the food for six weeks would be tough, but four weeks is just possible. Having a store somewhere halfway through the hike makes things a lot easier. Many stores carry quite reasonable pancake batter mix as well. Of course, if you can rely on catching enough fish, you can cut down on the food you must carry. Mostly I don't rely on it, but fresh fish is major, major, major YUM in the midst of dried foods. In the autumn, the forest is also full of berries and mushrooms—but I really don't like the latter. And there's no substitute for pancakes. Mmmmmm, pancakes. Pancakes are gooooood. Remember to eat pancakes. Pick ripe cloudberries, add the tiniest bit of sugar, and eat over pancakes. Yum.
Here's the pancake mix, enough for a sturdy evening meal plus breakfast the following morning (for one hungry hiker). I guess you could utilize dried egg in there as well, but I've always just used extra powdered milk instead. Two of these servings will almost fit in a 1 liter bottle. Better to make generous servings, and what doesn't fit in the bottle can be sealed in a plastic freezer bag.
Sometimes the best you can get is a ditch or stream leading out of a swamp. Or perhaps even a natural or dug-out hole in a swamp, where water collects. A swamp can harbor various signs of life, but mostly they won't kill you either. I've drank out of swamp streams and survived. If it looks ok, doesn't smell bad, and doesn't taste bad, then the water is probably ok to drink. But if there's any concern, I've never taken the chance—boiling the water first (either make tea for drinking immediately, or boil the water and let it cool down for bottling) makes it safe to drink, period. There's also all kinds of chlorination tablets and purification filters on the market, but I've never bothered to look into those.
On occasion, there simply is no water available in the near vicinity. Quite often you can find some water regardless, but it may be too nasty to drink without boiling (which is a hassle) or even after boiling. Check your map to see what kind of streams or ponds your planned campsite has nearby. If there just is no water nearby, you will have to carry it from the closest available supply. I always have a 1 liter canteen with me (not always full, if I'm hiking where there's good water everywhere), but that's not enough for making dinner and breakfast when camping overnight. I have carried water in the pakki, by filling a plastic freezer bag with water (I always have extra freezer bags with me), tying it off and fitting it inside. That works also, but I recently realized that an extra plastic water bottle does not actually weigh much at all—it only takes up space. But space is at a premium in my backpack as well... However, if I store my pancake mix in the bottle, that space is not wasted. Now, if I ever need to carry more water with me in any kind of emergency, I can just transfer the pancake mix into a freezer bag and voila, I have an additional 1 liter bottle to carry water in!
Note that I cannot guarantee the safety of any water you choose to drink in the wilderness or elsewhere. The suitability of available water for drinking does depend on where and when you are hiking, and under what conditions. It can also depend on luck. There may be a dead moose rotting away just 50 meters upstream from where you stopped to quench your thirst. So drink at your own risk.