I was asked to post a photo of my usual luggage, so here it is. The pack on my back has about 20 kg in it, which is way too much. One reason is that I have seven books. If you travel like this, you can probably get by with two books - one Lonely Planet guide for where you are (I think these are the best guides for backpack travel) and one reading book. Most hostels have book exchanges.
I have way too many clothes, too much first aid stuff, and other things that I could buy if I really needed them. I think I could have gotten by with a pack less than half the size of what I have.
For a several month trip like mine, I could have brought the following: Three shirts (one long sleeve, one tee, and one short sleeve), two shorts, one pair pants, three pair underwear, three pair socks, one pair shoes, sandels, very light sleeping bag, light jacket, a few medications and bandages, foot powder (many travellers start to smell like feet!), small towel, sunglasses, cameras and chargers (I have three cameras), torch (flashlight), guide book, journel and pen, sketch book and pencils, and swim suit. Add a passport and a couple of debit cards and you are good to go. Should be able to keep that load down to 10 kg. I also have a small day pack to carry my camera, passport and papers, and other essentials. It is smaller than a typical day pack - more like a camelback - and I have found I can live out of it for several days if needed, maybe even a whole trip if I had to. I also have a light blanket that I got from a Royal Jordanian flight that I use to keep warm on overnight bus trips. And I brought a small ACER netbook computer to store photos and access the internet where I find wifi (pronounced "wee-fee" many places.) I have gone through five pairs of sunglasses now. Buy a guitar along the way and make new friends. There you go Tarelle, I hope that is what you were looking for.