Please keep in mind that the feedback you get here will vary from the general traveller. We're frequent travellers and are used to different things when travelling.
My stays at airports are usually short given that I'm one of the first people to board the plane. I always board as early as possible to make sure I have space for my carryon.
Some airports actually do things very well. To me, the airport should be functional. The thing that make a good airport are elite status security lineup (I abhor those that don't have this), clear directions on gates, comfortable seating, Starbucks (I like consistency), TV's with CNN, comfortable seating and internet. I have a lounge membership so much of this is already taken care of regardless of what the airport has. I also like moving walkways when walking and in case I'm stuck there at least one night place to eat.
Things I hate are airports that are overly spread out (Minneapolis), don't have moving walkways or are missing the above items.
To answer your questions specifically though:
While waiting for a flight, what do you do or wish you could do to pass time?
Work out and/or shower facility. I'd love to be able to lift some weights while stuck at an airport. Alternatively, grabbing a shower or nap (as they offer in Narita) for a reasonable price would be awesome. It would let me leave from Seattle to Newark without grabbing a shower in the morning (get one the night before) and I could get the plane grime off before my connection.
What do you love/hate about spending time at the airport?
I'm pretty numb to it plus I can hang out in a lounge. Most often it is lack of seating and crowds that bother me. Chicago, from what I recall, can get pretty packed at the peak times of day. Lounges are great, but snacks at some could be better, but this isnt general airport design.
Without any limitations, what would make the experience less stressful and more enjoyable?
Moving walkways and making it easier to get around is nice. Reasonably priced food and drink wtih nice variety is good. I was at a coffee shop the other day and they wanted $4.75 for a Perrier. It ruined my experience at the airport entirely. I wasn't paying for it personally, but would be damned if I would pay that much. Keeping food in line with local prices would be good. Some airports, such as the one in Calgary do this. Maybe some sort of book exchange might be good.
What do you bring with you in your carry-on?
Work clothes, gym clothes, toiletries, casual pants. I can usually use my dress shirts and casual shirts by untucking them at night. I keep receipts in the bag. Usually a phone charger goes in there too and my car keys once I leave my car.
....or ANYTHING else you can think of.....
Proximity of parking. In Seattle, you land, walk straight out to parking get your car. Not sure if all other airports are the same, but ease of getting out is great. I'm in my car and on the road about 10 minutes after we land. Also, as before, status based security lineups are my #1 favorite thing. Having to be at the airport by 6am instead of 5:15am is HUGE.
Thanks so much!!!