We've traveled and lived abroad with dd since she was 5 mos., but that's such a broad question, it's hard to answer. Do you mean what to pack to keep them occupied or what to pack for more practical purposes? I'll try to share a bit of what's worked for us.
For carry-on, bring things that you know will occupy them during awake hours. Make sure you have plenty of disposable diapers for the younger, as there can be delays. Make sure you bring some snacks and water (can be purchased for an arm and a leg after security). Changes of clothes for everyone, including yourself.
The older can probably be occupied mostly by the in-flight video and books. We limit screen time at home, but when traveling, throw out the rule book. The younger will have to be occupied the entire awake time. Plan around whether or not you'll be sleeping on the flight (I'm assuming at least some for both pan-pacific flights). New toys are nice, but realize that they won't occupy them the whole time (they will quickly get bored) and some of the old favorite toys might be a better choice. At 1 year, dd was REALLY difficult to keep occupied on a 13 hour flight. At 4, 5, 6, it was a breeze, as she could read or be read to. She's 8 now and we're headed to Italy this fall and I figure books and videos will keep her content.
I'd concentrate more on what to bring for the little one than for the older one. If the older one is reading, that would help. The little one should have a carry-on allocation, but if you can keep the carry-ons to the minimum, it really will make life easier. The last thing you want to be doing is lugging a bunch of stuff in addition to managing the kids.
Good luck and have fun!
Also... if I could just offer one other piece of advice. When they bring meals, they bring out the special diet meals first. That means if you choose a vegetarian meal, for example, you will have time to eat before the general meal service starts. If one of the adults orders the special meal, it will free you up to help with the kids during general meal service because you'll have finished eating and be able to have your tray table free. Also... the kid's meals are atrocious. If you care at all about your child's bowels, beware the child's special meal.