Keep it Simple
There are two rather low-tech solutions that deserve a mention. First off, a portable storage solution can be a lifesaver, either a USB key or portable hard drive. Backup all of your important files to portable storage device before you leave, and backup again periodically while you are traveling.
Secondly, if the majority of your work is documents and spreadsheets, then you owe it to yourself to consider using Google Docs. It keeps all of your documents organized with your Gmail account online, and allows for access anywhere there is internet access. In addition, if you use a browser like Google Chrome (or if you have Google Gears installed), the support for offline editing, and keeping local copies of your files sync to your computer is excellent. Check out Google's Blog for an article on using Google Docs Offline.
If you have multiple PCs and/or handhelds, then a service like SugarSync , Syncplicity or DropBox might be the right answer. For a reasonable fee, these services can keep all of the files on your laptop and desktop synchronized as well as maintaining a remote backup of your files in "the cloud", which simplifies access from mobile devices.
This option is great for users with multiple office locations, and multiple computers. Check out PC Magazine's review of these three services for a more in depth comparison.
Remote Access Services
When you absolutely must have access to your home machine, services like GotoMyPc and NTRconnect can be invaluable. They also serve as a great last line of defense in case you forget a file, or your portable drive fails. These are VNC (virtual network connection) style solutions that support virtually logging in to your home computer over the internet, taking control of your machine. In addition both support transfering files from your home machine to the remote machine you are using.
While both NTRconnect and Gotomypc have similar feature sets, NTRconnect has one distinct advantage offering "Wake on LAN" support, meaning that even if your computer gets turned off, or is in power saving mode you can turn it on remotely and connect to it. This solution is ideal for users who want a high level of flexibility, and are willing to pay for an easy to use solution, however I would not recommend relying solely on this solution, as you are at the mercy of your home office's internet connection, which is most likely fine 99% of the time, but eventually may fail when you need it the most.
D.I.Y. VNC Solution
If you aren't comfortable installing VNC server software on your home PC or configuring your router's firewall to allow SSH and/or VNC traffic, then you may want to skip this section. It's an approach that requires a fair amount of technical skill, and carries the same disclaimer mentioned above.
If you are technically savvy, this shouldn't be too difficult. UltraVNC and TightVNC are two popular opensource options for Linux and PCs. For Macs, there is a built in VNC Server, also Vine VNC server is great, and both Jolly Fast VNC and Chicken of the VNC are great VNC clients for the Mac.
If you do run your own VNC server, consider also configuring an SSH server for added security, as VNC is a very trusting and unsecured protocol. Life Hacker has a very basic VNC tutorial here, and Erik J. Heels has a good tutorial on his blog for setting up SSH on a Windows XP machine and and tunneling in to a VNC server. Some other resources worth mentioning, Red Hat Magazine has a good article on SSH config files, and James Stocks has a great SSH for Mac tutorial.
Regardless of your technical skills, one of the above solutions should fit both your needs and your budget. Leaving your office doesn't have to be stressful. If you think ahead, you can access the things you need most - even from miles and miles away.
The freelance lifestyle is an ongoing mix of challenges and rewards. Balancing the two sides of the equation can help keep your freelance work from invading your personal life, and make for a happier work from home experience all around!