I was wondering if I could use my camera’s SD card as an emergency flash drive for storing files from my MacBook.
If you can mount the card on your MacBook, then yes – just drag files to the card mounted on your Mac’s desktop. Doing that can be the tiniest bit tricky, however, depending on the MacBook you own. For example, my MacBook Pro has a SD slot on the side as does the 13in MacBook Air (but not the 11in Air). So it’s a simple matter to eject the card from my camera, jam it into the slot and copy files to the mounted card.
If your MacBook doesn’t have such a slot, you could try connecting the camera to the Mac via a USB cable, but not all cameras mount on the desktop (thus granting you access to the card) via this method. In such cases, it’s worth your while to carry a card reader with you. With such a doodad you jack one end into your Mac’s USB port and insert the SD card into the appropriate slot on the device (some readers support a variety of storage card formats). Of course if you have the ability to carry a card reader, you might just pick up a regular ol’ USB key drive and use that instead.
Note that while copying files other than those intended for your camera won’t hurt the card, you don’t want to fill the card to capacity with such files if you hope to continue to use the card to capture pictures and videos with your camera.