I have travelled o/s to Europe and in Oz with my 2 sons when they were bubs and active toddlers. The travel part was not that enjoyable, but here are a few things I found useful:
1. Less is more- I can't stress this enough- try to travel with carry on bags only (it can be done!)- it really is awful lugging bags and stuff around when you have to get on and off transportation. Backpacks or a small carry on hard case on wheels that match the airline's measurements is the best option- you can usually take 1 extra bag if you have a child. Also, you can get straight on and off withour waiting for luggage- bliss.
2. Don't take the car seat- it will take up the whole plane seat and there will be no room for him to sleep. a harness that fits the plane seat is a good option if you can find one.
3. I am super strict with the kids when on planes- zero tolerance- no getting out of seats unless for toilet and definitely no standing on seats or playing in common areas- hey, may as well try and set the standards early. It doesn't always work out perfectly, but worth a try.
4. Take alot of smacks that your DS likes, and a few new toys (saved up until nothing else is working) is a great idea.
5. Expect odd sleep patterns for 3 or so days at either end.
All the best for your trip.