In order of interest to me:
1 The tower frequencies, at O'hare this will be a steady stream of traffic
2 The frequencies for the airline you are flying
3 CPD at the Airport
4 TSA or a Federal VHF Limit Search
5 Find the nearest Starcom tower, you're in /\/\'s backyard and there's the Tollway ISP, ISP Chicago, many local PDs and FDs and if it's daytime probably some radio techs, all using the system around you, when I travel I always drop in a few of the locals public safety items into my scanner, it's fun to hear how it's done in the rest of the country.
And you've clearly never flown through O'hare before, you'll be late getting in and even later getting out, so make sure you have at least the first two points I mentioned programmed in if you want to know if you'll ever get out.
While I've had some major delays there it's by far not the worst I've had time wise or even as far as having things to do, but bring an extra set of batteries just in case.
