A quick word about formatting
I am a firm believer that you should not "clear-up" a card by erasing the individual images either in camera or via your computer, but should ONLY erase a card by formatting the card in the camera and not in the computer.
Images are organized on a CF card (and most all digital storage) via something called a File Allocation Table (or similar, like NTFS). The FAT--as it's called--contains the information on the size of the file, the location of the start of the file, as well as other housekeeping information. When a CF card is formatted, the device doing the format basically creates a new, blank FAT and writes that to the card. Now, while FAT is standardized (FAT32 is the most commonly used version), there are even different "flavors" of each version that, while compatible, can cause issues when intermixed. Your computer (whether PC or Mac) uses it's specific flavor of FAT, while your camera most likely uses its own flavor. To help prevent these mixed-flavor issues, it's recommended that you format the card only in the camera, and not the computer. If you do format the card in the computer, make sure you format the card in the camera before using it.
While a formatted card allows the camera to start writing the files to the newly-open spaces in sequential order, if you erase individual images and continue to shoot, you can run into the situation where the camera needs those recently freed-up areas for writing. However, since no image file is the exact same size, you can run into the issue of needing all of one "erased spot" and part of another. This fragmentation can cause issues; not big issues, mind you, but issues non-the less. And while there's nothing wrong with "chimping" out some bad OOF shots and continuing to shoot, I wouldn't manually erase most of a CF card and refill it up. But that's just me.
Single shooter card management
When I'm the only photographer, my card management system is fairly simple and revolves around six basic concepts:
- Cards that aren't in a camera are in a Think Tank Photo Pixel Pocket Rocket (PPR)
- Cards in the PPR are organized by camera (two cameras, each gets a column, and I rarely shoot with more than two cameras)
- Cards in the PPR are known to be blank if the brand label is visible
- Cards in the PPR are known to contain images if the back-side with my contact info and card numbering labels are visible
- The PPR is connected to my person at all times via the strap and an optional small caribiner
- Cards do not get formatted until at least two other copies exist (generally the main hard drive and an external USB hard drive, if not two USB drives)
That's the "shooting" part of the card management system. I also have a step that lets me track which cards have been downloaded by turning them sideways in the PPR, but you could easily re-format the cards (in camera, of course!) after confirming two copies exist. However, I don't format a card until I absolutely know I need it again, giving me that extra copy of all the images.
Recordable optical discs and other media
Now, some people like to use recordable CD and DVD as a back-up copy. Personally, I'm not convinced of the archival qualities of these discs. While I do use recordable CDs and DVDs as distribution of digital files to customers, I don't recommend long-term storage of the files on the discs. The two main causes for data degradation (also known as "bit rot") is heat and (sun)light, both of which are hard to avoid. And while there are "archival"-grade recordable DVDs and CDs out there, it's hard to beat the cost of external hard drives.
Multi-shooter card management
My multi-shooter card management is similar to the single shooter, but tailored for the specific needs of an event photography company with multiple photographers. First, a PPR isn't used; instead, each photographer is given the number of cards he or she needs for the event. Computing this number depends on the event itself. Gymnastics lends itself to fairly easily be able to judge not only the number of cards needed for each photographer, but the size of the cards as well. Cheerleading, however, requires a different approach.
Each photographer is also given specifically labeled envelopes into which they put the full card(s). These envelopes are picked up by the card runner and delivered to the dumping station. Each envelope contains information describing the location and timing of the card(s) within, such as apparatus or field, rotation or team, etc. This information varies depending on the event/sport.
The dumping station dumps each card to at least two locations, preferably three, one of which is offline most of the time (using two USB drives where only one is installed at any given time helps).
After dumping, the cards are put back in the envelopes until verification of the files has completed, at which time the cards can be erased. Again, I like to delay on erasing any card until I'm absolutely sure I can erase it, and then only if I need it.
A quick word about card sizes
Personally, I like smaller cards, 2GB or 4GB. (I even have several 1GB cards that I use for events, as I often rarely use up more than 1GB on a card until it's swapped for another, purely for organization.) Usage of smaller cards generally means less expensive cards (2GB and 4GB cards often go on sale at close to 50% off prices) as well as the added benefit of eliminating the "all the eggs in one basket" issue.
So, that's the basics of my CF card management system. There are other little things I do to help organize for my specific needs that wouldn't be appropriate for most readers, so I've left those out. As I said above, feel free to tweak this to meet your needs, or start with something completely different. However, make sure you have a CF card management system, or else you may be replacing a very, very expensive card one day!