About rescue disks recorded onto USB sticks

Hello,
One of my friends has complained about a virus problem on his computer. He has no internet connection, so I thought of creating a rescue CD for him. Read about both Kaspersky and Bitdefender from their sites, and found that both of them offer a rescue CD that can be recorded on to a pen drive. They can then be used for booting. My question is, if i create a bootable USB in this way, can I also use it for storing files, as I always do, or can it only be used for running this anti-virus? Thanks.

If there’s room left on the stick, you can store anything you want.

If I were you, I’d also burn a copy of the rescue CDs onto CD/DVD.

Making bootable USB sticks can be tricky, and you won’t know for sure if your USB stick is bootable in a certain pc until you have tested it in that pc. Some pcs are very picky about USB sticks when it comes to booting, some USB sticks are difficult or impossible to make bootable, some programs are difficult to make bootable on a USB stick, and there are several “standards” for making a USB stick bootable. All this makes it unpredictable as to what will boot on which pc.

Thanks.
The reason why I thought USBs can be good is because the updates that are necessary for anti-virus software. You can’t update a CD. But now it seems that even if it were a USB stick, the updates are temporary. They are not saved. After use, the program just reverts back to the original state. Or is there any software whose updates remain on the pen drive?