Let me offer you some peice of advice.....and insights into IBM...Since I have been with IBM Business Consulting Services(BCS) for the past 3.5 years and prior with PWC for another 3 years before IBM brought them out....So this is how IBM BCS operates their mobility employees(which consultants are one).

BTW - which practice are you joining?

With regard to alliance programs....Don't worry too much about joining your favourites right now.....IBM has its corporate travel policy, so the choices are limited...
Car rental is with Hertz, and you cannot collect points wiht the IBM corporate plan. (sucks).
Airline, you will have to purchase the lowest corporate fare, for US, typically its American or United.
Hotels, you have more choices, there is usually a negotiated rate with the client, IE. $150 a night. And the consultants can choose a hotel of their choice as long as its within that limit....Most consultants use Hilton, SPG or Marroitt.
All airline bookings needs to be done through AMEX traval with your Corporate card....And you cannot collect AMEX points with the corporate card...(another sucks)

IBM will re-imburse you for the travel from you home to the airport and from airport to home. This can be Taxi/limo or mileage for the drive and parking. Your choice if you want to drive or take the taxi/limo.

IBM will also pay for any out-of-state taxes you have you have to incur. Typically, if you work in one state for more than 11 months of the year, they will make you work off-site for 1 month, so they don't incur taxes.

As for staying with your parents or moving to NYC......Why not stay with your parents for now...and travel a bit and see what cities you like.
IBM has the flexible travel policy.....You don't have to fly back to your home city if you don't want to.....You can either, fly someone down to the work city to visit you....Or you can fly to a different city, as long as the airfare is the same....So if you like NYC, you can fly to your work location Mon to Thursday, then Thursday night fly into NYC, and monday fly back to the work location....
that way you get to see different cities, then you can pick which one you like to move to...

Food reimbursements, its not as good as you think.....There is a published per diem rate for all the cities that you work in and that is the per diem you get for the day. Atlanta was $38 a day.......So pick a hotel that offers free breakfast....as 38 dollars don't go far.....
On the expense report, you will just enter a per diem, don't need to itemize it......YOu will find tricks when you have more experiences to have your per diem go farther....(IE. take a client out for lunch, go with a partner or executive and have them take care of the bill, etc...)

Your cell phones will be paid for by the company when you reach Band 8....

Good luck with your new career...