Students will have to be pretty high level for this one, otherwise the concept will be lost on them or they just won't be able to participate effectively.
Print out the Diary pages, cut up and hand one to each student. There's a group number in the top left corner, tell them to find the other people in their group (4 in each group).  They each have a diary of their weekend with different existing commitments, and a personalised set of instructions to arrange plans with various other members of the group.  That's it really.  Once they've finished you can go round and ask groups questions like 'Which 2 people are playing soccer? What time?' etc if you want.
I've included a dialogue I drilled with them to practice some useful phrases for this kind of situation.  Might be some new expressions, like 'what are you up to?'.  Also on the 2nd page there's a list of the sort of phrases they might find useful to adapt for the activity, I think I just had these written up on the board but the handout is the crux of the activity, they just need to be high enough level.  I've also used it for a 4 person lower level teachers conversation class.