I'm a "belt and suspenders" kind of guy. I have backups on my backups and a spare even for those whenever possible. I hate to let a client down when something fails and it's so easy to come prepared. Extra cables, adapters and even amps are common to find in someone's go box. But here's a little item that few think of.
I got in the habit of getting out the manual every time I get a new vehicle and hunting down the page with the lamp specifications. I hit the auto parts store and get a two pack of each, staple them to a piece of cardboard and toss it in the glove box. It's a cheap and easy way to avoid getting a ticket for a non working tail light or flasher. It's just as easy for fuses.
The suggestion is to take an afternoon and go over every piece of gear you own and write down the specs for the correct fuses and then invest. Sometimes a blown fuse is indicative of a larger problem, but sometimes it's just a blown fuse and it's really frustrating to have to go dig through your glove box or drive to gas stations to try and find a replacement so you can have all your gear up and running.
It's cheap, it's easy, and it makes you look like a hero and a model of preparedness. Get after it!