Some absences are easy to plan for, like if you have a vacation and know you will be gone the first week of October.
Other absences, like when your first child comes ten days early, are easier to handle when you stay organized leading up to the big event.
Keep a daily workplan
Make a spreadsheet of all your cases that acts as a cheatsheet for what is happening and what is coming up. You can make columns for “upcoming dates,” “do now,” “waiting on,” and “do later.”
Yes, it gets a bit tedious to update it on a regular basis, especially when you swear you know what is going on in every case. At the same time, taking five minutes every day will make it easier to hand off to someone when you have to disappear for a day or twelve. The workplan will not solve everything, but it will help a co-worker get up to speed quickly on your cases.
Use an online collaboration tool
Sam pulled my arm and got me to use Basecamp. Basecamp is not designed to be a personal productivity tool, but a work collaboration tool.
I put all of my cases into Basecamp and also entered the big deadlines, so that either one of us can check in and see what is happening. If one of us has a question or comment, it easily allows us to do that and sends an email to either or both of us when a new comment is posted.
I was resistant at first, but it has worked very well for the cases we share responsibilities on.
Prepare for the unexpected
If you think you might be gone in the near future, but do not know exactly when, you can still plan for that. Like every other contingency plan, have it in place before the emergency happens. It is much easier on you and your co-workers when everyone has planned for you being absent.