I don't have a specific answer in terms of luggage. For carryon, we had iPads so the kids mostly played with those, although I did also bring some activity type books to help keep them occupied. In addition, I pretty much packed a lunch and snacks for the kids because one of mine has food allergies.
Even though mine were (newly) potty trained at the time, I brought a couple pull-ups just in case we weren't allowed to get up to go to the bathroom when the kids had to go. They don't always think ahead about those things. :-)
Also, I found the fruit chew snacks can help the kids with ear pressure issues when landing. I don't know if it helps pop the pressure completely, but it at least distracted my kids that they stopped talking about it and just ate their food. :-)
My kids are still in 5-pt harnesses so when we travel, we bring the seats with us. We used the GoGo Kidz attachment to make the car seats into strollers so we can haul the seats and the kids around that way.
When we did long term parking from home, my husband dropped me, the kids, luggage, and seats off at the airport and then he went and parked the car in the long term lot. It saved us the trouble of having to bring the kids, luggage, and seats onto a shuttle bus from long term parking. On the arrival side you could try that as well and have someone go get the rental car and come pick the rest of you and luggage up.
We actually had extra car seats so on the home side we could leave the attached seats in the car we were parking in the lot and put the other seats in the trunk. It made it easier when returning home because we didn't have to attach the seats we traveled with.