Yep, you an take your own snacks on board but at the other end you might have to dump them if they are fruit or dairy etc.
They do have regulations about liquids now.
I always take some snacks because airlines acn be odd about the times they serve meals and if the childrens' body clocks say that it's meal time they'll crack it if they don't get something to eat.
Most long-haul flights have seat back entertainment and it always has a children's channel so if you let them watch the TV it will help them to pass the time.
I take pencils and paper but only 6 pencils and then I get a cup and the rule is one pencil at a time and it has to go back in the cup before they get the next one. If they drop a pencil getting it back can be a total menace - they roll so you end up scrabbling around the feet of the passengers behind you (since the plane is always going up or down hill they vanish to the end of the plane if you don't get it within a few minutes). Beofre I go I like to google 'name of country colouring in' and print out a few sheets with pictures of our destination for colouring. Your children might be a bit old for colouring in but I'm sure that you can find some on-line resources that you could use.
Activity books are great as well - all the dot to dots and so on keep them busy for ages and they only cost about $4 at Big W.
Etch-a-sketch is great because it's one peice so they can't drop the parts. Anything that has lots of parts is evil - they will fall down and there will be one part that you will never find again.
Book are good but they are heavy and you will have to cart them all around the airport when you change planes half-way.
I take some spare clothes in case of spills.
When you change planes try and encourage them to run around a bit - the excercise will help them sit still for the next leg.
Airline food can be a bit constipating so try to get them to drink heaps of liquid.
As soon as the plane is full and before it takes off have a look around for an empty row and if you see one stake a claim straight away - having more space so they can lie down makes a huge differance.
Wheelie bags are great for kids because they're much easier for them than back-packs etc but my boys make me drag them after half an hour *sigh*.