I haven’t backpacked around the world, or for as long as you’re thinking, but I did go for about 3 months 3 years ago. I spent about a month in West Africa, a month in East Africa, and a month in Central/Eastern Europe. I had different friends accompanying me for certain portions of the trip, and for some portions I was by myself. I never felt afraid or threatened, even when I was by myself, but of course I was always on guard.
Transportation: I flew from West Africa to East Africa, and again from East Africa to Europe, but otherwise I got around by the cheapest means of transportation possible: local buses and “bush taxis” in Africa, and buses and sometimes trains in Europe. I also walked a lot instead of taking taxis, to save money–for example, if the bus dropped me off in the north end of town, and the place I wanted to stay was 8 miles away, I would always walk instead of taking a taxi (if it was safe, that is).
Food: I was on a super tight budget, and I ate local, inexpensive food whenever possible. In Africa, this meant eating “street food,” i.e. food prepared by local women on the side of the road that cost about $0.25 for a meal. In Europe, I tended to buy food from supermarkets and eat it in my room, or else I bought from farmers’ markets.
Clothes: I think I had 2 pairs of pants, a dress, a skirt, and a couple shirts. A light jacket. Flip flops, and sneakers, I think. It was plenty. I carried around a bag of detergent powder with me and washed my clothes at night whenever I needed to.
Lodging: I carried a tent and sleeping bag with me, which made my load kind of heavy, but it was definitely worth it, because it allowed me to save a lot of money on lodging. A lot of hostels have a camping option that’s much cheaper (and sometimes nicer–more private) than the dorm option. In Europe, a lot of people rent out rooms in their homes, which are cheaper than staying in hostels.
Budget: For 3 months I think I spent….$3000? This was 3 years ago though, and that includes all my airfare. Europe was much more expensive than Africa, of course–even the hostels could get pricey n the cities.
Anyway, those are my details. You should definitely go for it!!
P.S. language barriers! I only speak English (and a West African language, which was useful in West Africa, but nowhere else) and I was fine. It’s kind of embarrassing going to a country and not being able to speak the language, but I’ve found that there’s pretty much always SOMEone who speaks English everywhere. It’s always possible to get your most basic needs expressed just by pointing and miming, when all else fails.