definitely extra socks/boxers. did a lot of backpacking in hs, not as much in college. depending on the terrain youre doing (urban/trail) good footwear is a must. i always wear 6 inch boots on trail just because i like the protection, but if its more urban, a sturdy pair of gym shoes are a good option. as far as clothing, in the midwest I am pretty safe with a synthetic tshirt to wick moisture, a mid layer (patagonia nanopuff, snap t), and a rain shell. throw a hat in for sun protection/rain. bring atleast 2 nalgenes, more depending on if the campsites are dry/how far a water source is. I like to pump water vs iodine tablets, but they arent the end of the world. think of things that have multiple purposes to cut down on weight/trash... toilet paper can also be used to dry things/also a firestarter in a pinch. roll up a jacket and use as a pillow. some ultralight tents use trekking poles as tent poles.
most of the gear I get from REI garage sales, where they sell used gear (usually just tried on and the customer didnt like) for relatively cheap. picked up some asolo boots and some patagonia shorts for like $60 total instead of 200 retail.