I've been so lucky (compared to people in previous threads here) as I get a couple of months usually out of a cartridge in my Fusion. I rinse it off, let it dry if there's time, and will usually wrap it in a piece of paper so the blades don't get bent when I toss it in with all the other stuff. In the travel bag, I've changed the blade way more often because they were damaged in the bag than because they were no longer doing their job, so now I try to protect them a bit.
If you google
travel razor holders
you will find options for plastic covers to protect the blades.