gneiss, congrats on grad school! I'm finishing up my BA now and am making plans to either attend grad school (to become a legal constitutional researcher) or law school.
I used to have serious problems on my third day when I first tried to stop using. The key for me was to make plans ahead of time that kept me busy on that day. The one that worked best and got me through the final time was a movie that was only shown a few times. I made plans to go with friends, and then out to eat at the burger joint next to the theater that night. None of us planned to drink since we had classes and/or work the next day. It also kept me tied up with plans during the tempting time when I normally would use. Also, others were expecting me to be there and would be disappointed if I left during our activities.
Now that I type this, I may use the same technique to get through the third day of non-smoking. I've quit several times lately and fallen back on, surprise surprise, the third day.