Windows: Nothing beats a full-on system backup for making sure you've got duplicates of all your important stuff. Free utility Back4Sure is a simple but powerful tool for quickly, incrementally backing up important files to external drives from anywhere.
Back4Sure doesn't care if you're backing up four or 4000 files, it quickly organises and ships them to the target directory of your choice. The app automatically compresses files into a Zip or 7Zip file format to save space, a great feature for saving space when you're using a flash drive. One of its coolest features: You can set Back4Sure to work with a specific external drive (portable thumb drive or large external drive) by name, and it will remember that drive regardless of what letter it's assigned when you plug it in. (Anyone who uses a thumb drive often knows they can often be assigned different drive letters depending on how many other devices are plugged in.) It also does incremental backups, so backups following your initial one should go relatively quickly.
It's easy to choose which files you want Back4Sure to include in a backup — just select them from the tree-view displayed in the app's preferences panel. Filters make it simple to include or exclude files, and the cleanup feature alerts you to orphaned files that don't have corresponding source files anymore so you can quickly delete them.
Back4Sure logs everything it does in a plain text file, but users can opt for a second format optimised for automated analysis. You can even create a link on your desktop to a previous backup job that can be activated and re-run just by double-clicking its icon.
Back4Sure is freeware, and only works on Windows. Got a killer app you like to use for making quick and portable file backups? Let us know in the comments.