Hi there! The easiest thing for you to do would be to experiment with packing and find out what sequence works best. I usually put my shoes at the bottom, roll my clothes (sometimes I'll roll two shirts together), and put any miscellaneous crap in plastic bags. And anything that leaks should go in its own baggie since cabin pressure can do funny things to bottles of liquid.
I usually bring a book and mp3 player and *maybe* a deck of cards for a long flight. You might get lucky and score a plane/airline that has the individual screens for each seat, which is nice because usually there is a list of movies to choose from.
And as for locking up your pack, well, it's going to depend on where you're staying. Probably most will have security lockers that you can put your pack in. If they don't, locking it to your bed is not a bad idea. I would NOT (!) leave the video camera at the hostel if I were you. Keep it on you at all times. If for some reason you absolutely, positively can't take it with you, check if your hostel has a "safe" place you can stash it. But don't count on it. Plan on keeping it with you.
I hope this helps! Good luck!!