S.R.
We went on 10 round trip flights with my daughter in her first 14 months.
1) All hotels have cribs/pack & Plays for them to sleep in. We bring all the 'lovies' from her crib and she almost does not notice. (She has 1 bear, a small 'taggie' and a blankie)
2) Hopefully your son will fall asleep on the flight but if not...... Bring LOTS of snacks and travel size toys and be ready to pass him back and forth between you and your husband. You NEVER know when you are going to be trapped on a plane so think about liquids and food. TSA is tough to get through with certian liquids. Check that out.
Most airplanes have a changing table above the toliet (depending who you fly, you can call the airline & check what type of aircraft and ask them) and there are some changing tables in OHare.
3) stay in the same hotel as the wedding - NO matter the cost. TRUST ME!!! When it's bedtime you can take him up and an hour later, you husband can come up for an hour, then you mom/aunt... So nobody misses much of the wedding.
4) Don't worry about the time change, it seems to work itself out. You might be a little off but it never seem to be a big deal.
5) bring a good stroller! So you can enjoy yourself a bit.
I never rented anything - You need a carseat to get to the airport. I bought a travel 'highchair' from One Step Ahead ($19.95) and it packs like a lunch box and you can take it on the go, even in the park! The stroller you can gate check and pick up the second you get off the plane.
Hope all this helps.