Always pack food and drink on a bus. You never know the schedule. The last greyhound I was on in America had regular stops with marginal food every couple of hours; but this is not a guarantee. I always carried a bottle of water, some snacks, chips, cookies, candy bar, and a book to read. I recall one China bus where the first scheduled stop was 8 hours after we got on the bus! (Yes, there were was a bathroom on the bus.) I have also had bus trips that just happen to take about 24 hours too long.