New clips available on 'Wing Clips' include scenes from the new Pixar movie 'Up'. If you do need new inspiration for an end of year assembly, you could take part of the story from this movie as a theme for talking about unexpected adventures.
Something I find is that children/young people going into the summer holidays are so excited for them to begin, and then for some, after a week or so, they're really bored and are wishing they were back at school again. There's some clips you could use on wingclips from this film, but probably more helpful is looking at the story itself. Here's a quote from Director/Writer Pete Docter:
"We came up with this image of a floating house held aloft by balloons, and it just seemed to capture what we were after in terms of escaping the world. We quickly realised that the world is really about relationships, and that's what Carl comes to discover."