Thanks for your help. Alas I'm flying cattle class. *awaits banishment from forum*

I do have a laptop bag within the required dimensions, so I might go with that instead of the backpack; their website says nothing about different restrictions on hand luggage varying on class of travel. It also says nothing about food, glassware and chargers for phones/cameras - presumably all ok in hand luggage?

Buying a bigger bag in the USA is definitely a good idea. Although I could possible shove the backpack in the carry on bag for the journey out. I'm thinking put everything I actually need in laptop bag and everything else in carry on bag so that if the carry on ends up in the hold it won't be too disastrous.