That's a great question! I love doing mixed city/wilderness backpacking when I travel for long periods.
What: The idea is to spend months going back and forth between civilization and wilderness. Moreover, you don't always have to stay in a hostel/hotel when you're in a city; you may want to camp in the city. Some call it Stealth Camping in civilization. My friend Bernie Wilt calls this ParaWilderness. I like to call it Urban Camping or Invisible Camping. The idea is not to camp like bum, who is often in plain sight and stays for an extended period, but rather to find an environmentally friendly, secluded spot to stay in for a day or two and then leave no trace.
Why: Some people have plenty of time, but little money. These people often seek to have the longest journey possible. They're rather spend five months in Europe and spend $2,000 than to spend five days and spend $2,000.
Where: Urban camping is best done in city parks. Nearly all cities have parks (many are quite large) and have areas that are deserted at night. Few walk parks at night and if they do they almost never leave the path. If it's an extremely dense city (like Tokyo), you might have to take a bus/train to a suburb, but this is rare.
How:To find a private spot, arrive at dusk (or at night), use a red LED light if necessary (using a bright light will attract attention), and set up camp as far away from a trail as possible. Do not setup your shelter unless you expect rain that night. It's much better to lie down next to bushes that will hide your presence. Camping in city parks is not illegal in many places, so the main reason to find a good "hidesite" is to hide from trouble makers. I've never had a problem, but I've also taken many precautions. Lastly, pack up and leave before sunrise.
Gear List: Since I'm in civilization, I often carry more clothes than I would carry on a pure-wilderness trip. I might carry one pair of pants, one fleece sweater, and one light rain jacket. 2-5 pairs of underwear/socks. Carry a light sleeping bag since you can wear the many layers you are carrying. Carry a tarp and pad. That's about it. I don't carry cooking gear since delis and restaurants are everywhere in urban areas. I carry one kg of food at most, often nothing.
Lighten Your Load: When I went through Eastern Europe in 2004 for 5 months I carried so much stuff that I needed two backpacks: a light one for the day and a heavy for everything else. The best way to lighten your load is to use the storage lockers in public transportation centers. Major bus and train terminals usually have lockers you can rent. I used them all the time.
Remember to be invisible, respectful, and leave no trace!
