I'm a big fan of 5 point restraints, so no booster for DS (almost 3)! In fact, I'd like to have a 5 point restraint for myself!
At home we use a Britax, but for travel, we bought a Cosco Scenera that has good ratings and is inexpensive and much lighter than the Roundabout. It was GREAT for the plane, he was very happy being in it, and it's simple to secure quickly into a vehicle.
We also bought a carry bag, it's some sort of tough fabric with a big strap. I think it's Eddie Bauer brand? Got it from Target for around $20. On our way home from vacay, it was just me and DS (DH was called away by ailing father), and while it was a pain to get through security b/c it had to come OUT of the bag (then back in), it was easier than trying to carry it (especially b/c I know, and can't un-know, that you aren't supposed to carry it by the straps) in my hands.
However, you don't HAVE to use it on the plane, and if you don't, you could just check it. Then again, baggage handlers + sensitive carseat that shouldln't be dropped or manhandled = perhaps not the best situation.
As for a stroller, we haven't traveled with one yet (just bought our first jogging stroller a few months ago) b/c I've found slings (and the Ergo as he got bigger) to be easier, but this time we will be traveling with a lightweight one, and I figure we'll gate-check it and perhaps use it to cart him through the airport. Who knows?
Oh wait, how are you getting from airport to DL, and will you be renting cars? If you're taking transportation like a bus that doesn't have seatbelts and therefore can't accomodate a carseat (or booster), perhaps you don't need to bring a seat at all? But maybe you are renting a car, and that's why it's in your thoughts.