iOS 9 and watchOS 2 are scheduled to drop tomorrow. Generally, Apple releases iOS software updates around 10 am Pacific/1pm Eastern. I've been running iOS 9 beta on my devices for a while now and have been very happy with the upgrade. In fact, David and I did an entire episode of Mac Power Users this week discussing the upgrade.
As always, prior to any major upgrade it's a good idea to make sure you have a good backup, or two, of your iPhone and iPad. Back in September of 2014 I posted a comprehensive guide for backing up your iOS device at is still good today (even if the screenshots are a bit out of date.) If you're planning to upgrade to iOS 9 tomorrow, it's a good idea to go ahead and backup your devices prior to the upgrade.
While I don't advocate preforming a major upgrade while you're away from home, remember that you'll need at least a 50% charge on an iPhone or iPad to start the upgrade and if you're planning to upgrade your watch to watchOS 2 you'll need to connect a power cable to complete the upgrade process. Might be a good idea to throw a cable and charger in your bag tonight.
Of course the safest thing to do is to give things a day or two to settle down, but hey...