The all important pack. When your on the road it's the only thing you have to keep your day from going to hell so it's pretty important to be well prepared. I was in a sticky situation and left my pack were I couldn't get it for roughly three days. Worst nights of my trip by far.
One problem though: I can't tell you everything you need to pack. You need to adapt as you go and prepare for your own situation beforehand. What I can do though is give you ideas for necessities that you can bring along.
~The bag: I recommend a hiking bag with some back support. Make sure it can comfortably sit on your lap for hours.
~Clothing: Pack for the weather. If you're on the road an the climate changes sell off some clothes to buy clothing to fit the climate better. No matter where you're going bring a jacket or a hoodie, it still can get chilly at nights and in the morning. CLOTHES WILL TAKE UP HUGE AMOUNTS OF BAGSPACE.
~Emergency food and water: Add in a couple water bottles just in case. Some can food is a good idea too if you can spare the space and weight.
~Shoes: Make sure you can walk ten miles without wearing your feet out. I still have marks on my feet from last time.
~Maps: When you're walking getting lost sucks.
~Chargers: If you bring a phone or mp3 player you need to charge it.
~ID: You're going to need it at some point.
This is just the stuff I carry with me EVERYWHERE. When I'm bunking at somebodies house or have a safe place to stick my stuff I make sure to always have this packed because you never know whats going to happen. I have a smaller bookbag that I walk around town with and keep my larger bag where I'm staying with most my clothes and gear I don't need that day. For a complete list of everything you could possibly need and a easily customizable packing list I use this site.