We have 2.5 year old twins along with a 7 year old. Our 7 year old did without the stroller when he was 5, although there was one time while we were waiting for the parade where he crashed in his sisters and actually fell asleep.
We are active, but we do need a stroller with the little ones for safety reasons, I really don't want to lose anyone.
At home we use a jogger that is quite big and bulky. The airline actually said I could use the double jogger and check it at the gate. I really can't imagine that, it is huge and heavy and although it works great for me when I am running in the park, etc, taking it to a place full of people, I would worry that I would be running into people with the front wheel.
I recently bought a lightweight double stroller used for $75 (this one retails over $300) and figure I can resell it and get my money back. Still cheaper than renting one and I'm sure I will get my money back.
But, as for packing them full of stuff, honesty I need everything we pack. If might be bulky for some, but I really don't want to car around anything I don't need, but it all adds up.
Diapers, wipes, sippie cups, water bottles, change of clothes, small snacks, and all the other things people need. I wouldn't bring in a huge cooler, but will have a small cooler bag to keep the milk in so its not sitting out in the sun all day.
I know there will be points where the kids will melt down, the problem being they won't nap it we went back to the hotel anyway, so we will push until they fall asleep and use that time for my older son to go on a few rides.