I recently completed a round-trip SFO-HKG on CX 870/879 and there were no sandwiches offered. The SFO-HKG is the more time consuming one because of the head winds and my flight was more than 14hrs. CX does provide 2 full meals but depending on traffic at SFO, you will definitely feel hungry sometime during the flight.

I have tried the cup noodles and its not that bad. Fills up your stomach and I personally prefer them over chips. You can go and have apple juice, orange juice any time you want.