Great suggestions from previous posters. O'Hare is a great airport, right up until there is a weather problem. Then it's "Welcome to Camp O'Hare". They actually have camp cots they break out if there is a large number of stranded people having to sleep in the airport.
Anyway, I cannot stress enough wait a previous poster said. If your flight is canceled for ANY reason, pull out your cell (or go to an airport courtesy phone) and call the airline. Have your booking confirmation and flight info handy, and ask to be protected (airline jargon for booked on the next flight) on the next available flight, and make sure they assign a seat. Then go to either a self check-in kiosk or a ticket agent and get your new boarding pass, then go to your new gate. If you wait in line after they anounce the cancelation, the later flights could all be booked before you can talk to anyone. Plus it saves you the wait in line!