depends. if your a youth a lot of places have youth outreach programs that you can take advantage of, like the YMCA. some churches do it too. clean yourself, clean your clothes, eat food, some places even have doctors for street youth thats quick and easy and free. im in canada though so its probably different in the states.
have a cotton layer and a fleese/wool layer over it to absorb moisture. I'd wear black or brown 'cause you're gonna be dirty for the most part. I prefer a good pair of hiking boots in comparison to leather boots or skate shoes 'cause when you're carrying a heavier pack a distance the support makes all the difference. Cotton socks with wool socks around 'em. You don't need much other than the nessesities of life; warmth, smokes and booze (if you need em, I dont) and food, and an instrument if you play one 'cause the road gets lonely and music can make you money. are you city hopping or gonna be camping? There's food all over cities wither its a handout or scrounging through trash. You'd have to be pretty dumb to go hungry in town. Get a good sleepingbag (like -10 or better) and a waterproof thingy for it so it stays dry. Something rainproof for you and your pack unless you don't mind getting rained on. I hate being wet personally. other than that supplies are easy to find, like cardboard for sleeping on. I like to have a toothbrush and a mini travel paste and a washcloth so I can wash my face in public bathrooms. Like mentioned you'll pick up things and drop other things off as you find what items are most useful.