Scavenger Hunt
This game is suitable for a coach bus since it keeps the passengers&' minds and eyes occupied while they hunt for specific items. Start by compiling a list of things that passengers are likely to see from their seats during the journey, such as cows eating, a sign with the word "no" in it, a red house, or a woman riding a motorcycle. Divide the passengers into teams, giving each team a list. The first team to spot something from the scavenger hunt list yells it out and gets to cross it off their list. The team with the all of the items crossed off their list first wins.
Trivia Games
Trivia games require some preparation before the big journey but they can keep you and the other passengers entertained for hours. For example, you could take questions from famous trivia games such as "Who Wants To Be a Millionaire" or "Trivial Pursuit" and cover questions in politics, history, current events, geography, and others. Alternatively, you can just make up your own topics to cover subjects that you know your passengers will be interested in such as architecture, cinema, music or travel. Consider providing a prize for the person who racks up the most points.
Categories
This type of game is suitable for bus trips since you can easily adapt it to a bunch of child or adult passengers. Passengers can play it while sitting in their seats and the more challenging it is, the more occupied the people riding will be. For example with young children you can start with a simple category such as vegetables. The first player starts by saying "zucchini" and the next player might say "lettuce." The next player might say "carrot" until you all exhaust all the possible categories of vegetables. The last person to think of a vegetable wins. With adults you can make this much more difficult by starting with a nebulous category such as celebrities with famous parents. The leader would start by saying something like "Kate Hudson" and then the acceptable following answer would be people like Colin Hanks, Freddie Prinze, Jakob Dylan and Ben Stiller.