This is most likely the last appearance of the Inbetweeners, as Bird, Buckley, Harrison and Thomas are all too old to continue playing these roles, and the original film was meant to close the series; but a sequel was only made due to popular demand.
The song Will plays on the guitar around the camp fire was originally due to be "You're Beautiful" by James Blunt, but Blunt wouldn't allow the song to be used in the film. Simon Bird, who doesn't play the guitar, spent 3 months learning to play "You're Beautiful" before it was changed.
The trivia items below may give away important plot points.
When Will and Katie are talking the night she and Ben get together Ben is playing the guitar in the background. The song he is playing is 'The first time ever I saw your face', the same song Will played to her.