Always have a back-up plan in case the player you were expecting to hinge a session on doesn't turn up, or the party choose to do something completely different than expected. It can be something simple such as a prepped wandering monster group - anything that will be fun to play and give you time to come up with more stuff. How much alternate prep is needed depends on your improv skills & tools (encounter tables etc), and how much prep the system requires. You never want to be in a situation where you tell the group "If you do that/don't do that I haven't got anything prepped, so no game today."
3e/4e Initiative Tracker
I hand round a lined piece of paper with the init numbers up the left hand side. If the possible range is 1-25, then 1 at the bottom, 25 at the top. The page has a central column, players each write their PC name there by the number of their init count. Ties go to left or right. GM writes his monster inits in last.
Status conditions etc can also be written on the init tracker.