It would help if you could give us the day of the week you will be here, plus your actual arrival and departure times. it's hard to tell from your post if you have already factored in time to take care of all the airport things--baggage claim, possibly immigration and customs if you are arriving on an international flight, etc as well as check-in and security the next day for your onward flight. Also, are you planning to sleep while you are here?

Getting around anywhere will be time consuming and costly, as our public transportation system isn't the best, especially in the night time hours. If you want to leave the airport area and you don't want to rent a car, you would have to rely on taxis, which could be problematic for your return to IAH, depending on your timeline.

It all depends on the time you arrive and depart. Say you arrive at 8:00p and depart at 6:00a. Then you can take a taxi and go to the Galleria Mall (my preference) or to The Woodlands. Both places have shops (that will close at 10:00p), restaurants / bars/ cofee shops etc. all within walking distance (also if at the Galleria - the water wall). That said, by the time you go through customs and immigration and get to the Galleria, it will be close to 10:00p and the mall (shops) will be closing. The taxi will be about $60.00+ and another $60.00+ to return.

The best option will be to see if you can get (buy) a day pass to the United lounge and stay in the lounge. I think most of the cafes and restaurants within the airport close around 11:00 or 12:00 too.