My husband's experience (he just flew out last week)
-When you leave MEPS you have your "packet" of info for when you arrive in Chicago, if there is a group of you leaving together, one will be assigned as "group leader" who will need to keep track of everyone. My husband was the only one though, so he didn't have to worry about it.
-Your packet instructs that when you arrive in Chicago, you need to go directly to the USO which is in Terminal 2.
-Depending on how long it was since your last meal and when the next bus leaves, you should have time to grab something at the airport with the meal voucher check they give you. (Normally USO facilities have food and drinks, but when my husband arrived at 7:30, they didn't have any).
-The bus to RTC departs every so often and recruits are taken in numbers of like 55 I think. You just have to wait for the next bus to fill up.
-My husband was able to call us and text while he was waiting, but had to turn his phone off when he got on the bus.
-When you get to RTC those that have cell phones can give the "I'm Here" call from the cell, you usually get a little more time from what I have heard over those that use the pay phones. My husband got about 2 minutes
I can tell you this was great being on the other end, so whoever you call will be happy too.
-Then after that, radio silence for a while.
-I would recommend eating a big dinner, since you won't be eating again for a while. My husband wasn't hungry but we told him to eat anyway and later he said he was glad he did. And maybe drinking a coffee or energy drink to get you through the next couple hours. You will be cranky and overwhelmed with everything at first.
-My husband slipped a little note in his box before they packed everything up and said it was 01:00 ish when they were doing that and he arrived at RTC around 9:30, so prepare for a long night.
**Hope that answers your question with a little extra thrown in.