Southern Califonia for 20-somethigns

[starfish19]

This will be a post and run so thanks in advance. A few friends and I are all heading to LA/San Diego to meet up for a reunion. A few of us have been to California before but for the majority it's the first time. Any recommendations or must dos?

[dearprudence]

What kinds of things do you generally like to do when you travel? What time of year will you be there?