Packaging a bike for flying with a bike bag
What?? 

No!

Hardcase, hardcase, hardcase!!!

Your bike is not going to fare well going most of half way around the world in nothing more than a plastic bag. Please believe me. Don't ruin your tour.

Some shops rent hard cases. Call around and see what you can find. Ask your friends. Ask local clubs. Look for a new or used one, buy it, and sell it when you're done. Ship the empty case to your endpoint.

For that matter, you'll probably be better off- both in terms of how the bike is treated and how much it costs you- if you pack the bike and ship it ahead of time. Just make arrangements with family/friends/local shop to receive it. Get it insured.

Whatever you do, don't ship your bike in a plastic bag. If you don't heed my warning, please post pics.