So I lost some laptops. Three. Three laptops. I got the last one back, but even if I hadn't, I've learned enough about the hell that that puts you through to have some advice if you end up unexpectedly computerless.
This one's a no brainer for anyone with a Mac. iCloud is free, and accessible from any browser. The only thing is, it needs to actually log onto a Wi-Fi connection for it to find your computer. So unless the lid's popped somewhere near a known network, you might be out of luck. Still, doesn't hurt to try. Free
Prey will give you a slightly better chance of recovering your laptop. It pings back to a web server, and if you're ever separated from your computer, it can give you access to on-board camera snapshots, screenshots, and activity logs. Free for up to three devices.
This is one of the big ones. You should of course back up your system regularly, but syncing your system to Dropbox means that everything you do should, in theory, be backed up. You can save your iChat logs across multiple machines to the same folder (or other clients by using Dropbox mods), and set most of your apps to save by default into folders within your Dropbox folder. This is especially useful if you work with a lot of lightweight text docs or non-massive spreadsheets. Free, upgrade to 50GB for $10/mo
You don't necessarily have to use 1Password following a laptop loss, but it makes nuking all of your passwords a lot easier than going through and changing them one at a time. $50
Let's say you had a lot of very sensitive data stored on that device. A clean sweep of the passwords is in order, but you've also got to plan for the worst and assume there's at least some chance that your doomsday files are out in the wild. Identity Theft Research Center is a good place to start doing research into how to set things in order if you think that happened. Free
If you can't afford an immediate replacement, a cheap tablet is a good place to start. It's amazing how much more time you have to enrich your brain with words when you're not looking at galleries of bunnies for 6 hours a day. And while the Fire has its share of problems, it's only $200, and has the whole of Amazon's ecosystem behind it. $200