I tend to carry a maximum of 1/5th of my bodyweight (including water and food) which is about 14kg, but preferably less, especially if walking long days. I would aim for much less if not camping or if not necessary to carry much food.
Some ideas on the following:
For me one of the most important things is having comfortable footwear. Also having good footwear and comfortable feet will help to prevent other problems such as knee and hip problems from cropping up when compensating. It is important to minimise blisters.
An important point is more weight on your feet is equivalent to carrying many times that weight in your backpack. For this reason I tend to go for the lightest footwear possible for the terrain. People who are less sure footed or less experienced carrying a pack on differing terrain may tend towards a firm boot with good ankle support.
So what type of footwear?
There are many types of footwear that people walk in: Sandals, trainers, hiking shoes, hiking boots. Finding the balance for yourself between cushioning/ventilation/support/weight/weather resistance is important.
My North Face Hedgehogs, great light weight shoes with a grippy vibram sole. Although I have suffered wearing these with a heavy pack and should have had more ankle support. Anything other than mildly bad weather and I would probably be wearing something more boot-like.
Ranging from an orange survival bag or emergency shelter on short/day walks to a tarp/bivvy bag/tent for longer walks.
I generally carry a tent on longer walks which allows me the comfort in the evening. It is possible to get solo/two man tents which are very light < 1.5kg/2kg. Doing a search on google will bring up many forums and discussions.
I use a Hilleberg Akto, one of the more expensive makes but would definitely recommend it for quality. I was lucky enough to get mine in a sale for a 1/3 off. The Akto is a one pole tent which can be pitched with 8 pegs. One of its drawbacks is that it is not free standing, on rocky ground this can be tricky and a little creativity is involved in pitching! If this is something that would bother you maybe look in to free standing tents with more poles (which may be heavier).
On some trips I have considered taking a bivvy bag if only for the flexibility it would give in stopping for the night (for example at some points on St Olav's way, Noway finding a decent spot meant quite a bit more walking in the evening).
The Hilleberg Akto....
The two main categories: Down or Synthetic?
In a nutshell:
Down is lighter and warmer for the weight. It also compresses well and lofts after being compressed. Looses most of its insulating properties when wet as the feathers stick together and do not trap the air (which is what keeps you warm). Synthetic is heavier, retains more of its insulation when wet. It is cheaper. It doesn't compress as well.
I use a down bag and carry it in a waterproof sack. This has sometimes got wet when bivving and I would recommend a synthetic bag for this.
After many years of sleeping on a foam mat, I bought a ¾ length Thermarest Prolite 3. Luxury in a bag! A foam mat, is however more reliable as there is nothing to puncture etc. but certainly heavier and does not pack down nearly as well.
An unfortunate incident but Thermarest did replace the mat without any problem. I was however without a mat for a while which could have been a problem in colder weather.
Try on many different types, find one which is comfortable and has strapping which is the correct size for you. It should rest on your hips when the hip straps are done up but not restrict hip movement. Getting one with an adaptable back system may be advisable so you can tweak it to your requirements. Many lighter weight materials are available but they tend to be more expensive. Mine has a capacity of 65L which I find is enough for trips of many weeks. A backpack cover is useful in the rain. I also put my kit in waterproof sacks.
I use an alcohol burner, namely a Trangia. I use a mini when walking by myself (a small pot and lid) and a Trangia 25 if walking with someone else (two pots, lid and base). Fuel is widely available in many countries. Alcohol burners are very reliable,clean to run and relatively safe although cooking times may be longer than gas and petrol alternatives.
There are some very good and light gas stoves such as the MSR pocket rocket. Although gas may be less reliable at altitude/lower temperatures if that is what you are planning, they also create empty canister waste.
Petrol stoves with pump bottles are good at lower temperatures and are very powerful – comparable to a gas hob on a home cooker. They are also harder to clean. I have seen them flare on occasions so extra care is needed around clothes/tents. (I've actually seen one flare and burn most of a tent away - but luckily no one was hurt)
Compass & Map
Having a 'silva' type compass and a proper map is essential when walking many trails especially in the mountains, even more so in winter. Learn how to read a map and how to use your compass, take bearings and know where you are especially in low visibility/bad weather. Consider going on a navigation course.