If you have not yet filed your taxes, today's assignment is to start the process. Either call up someone to schedule an appointment (make sure it is guarenteed, and shop around for quotes on how much it'll cost), or begin doing them yourself. H&R Block's website has a pretty good free checklist of things you'll need for doing them yourself or taking them to someone else.
If you've already done your taxes, decide if you need to make any changes for next year. Then call up your HR department/payroll, etc., and make those changes NOW. Don't wait another day.
Determine if there are any services you can do without: Cable, long-distance, text-messaging, webphone, gym membership, etc. If you can do without it...call them up right away to cancel. You probably pay for every day that you use it, but there's still time to get a prorated refund for March!