With regards to Jetlag, the flight to NYC is only around 7 hours max, i find the easiest way to beat it is to stay up till around 10/11pm on the first night and then get a decent night's sleep and then i've found it easy enough to get used to the time difference from there, with the gradual time difference when travelling across the US i've not found this a problem before, everyone's different of course

with clothes, i travelled from nyc-los angeles last june/july with stops in washington dc, nebraska, missouri and arizona in between (took a month) and only packed summer clothing, no trousers, just a light weight rain jacket (needed it a couple of times!)