Set targets. Manage people's expectations, and make sure that what they expect of you is reasonable. Warn the team how they may be affected by the change. If you're going to need help, make sure it's agreed at the outset.
Seize the day. Work out what you want to get out of the role. You have a set amount of time to establish contacts and make a good impression. A few clear aims will help you use the chance better.
Don't panic. You wouldn't be in this position if they didn't think you were up to it.
Get people onside. Pick your boss's brain to find out who your allies are likely to be. No need to repeat the mistakes your predecessor made as a rookie boss.
Treat the job as your own. Don't focus on how your boss does things, and stop telling everyone that you're 'just covering' the role. Make it yours.
What next? Before your boss sets off, discuss what you'll be doing when they get back. Will you get to 'keep' some of the more complex tasks, or will you be stepping straight back into your old shoes?
Think ahead. Make it an opportunity, rather than a disappointment.