i roll around alot. I throw in a few sprint, but over all i don't like over doing it for a warm up. An hour of z1 w/4 sprints is a good thing for a crit, 45 minutes w/ multiple balls to the wall efforts, not so much.
try this: 10-15 minutes z1 hr followed by 1 minute at a decent pace (think threshold), 5 minutes jra, repet the last step one more time, 1 30 seconds hard sprint (NOT ALL OUT JUST HARD), 5 more minutes of rest, one 15 second all out, 5-10 minutes of rolling around, stop to pee, get back on bike and ride to start line. (another 10 minutes or so).
Simple plan, not too hard, but you will get your engine running