I wouldn't bother with it unless I was going to be riding someplace where help was a long way off, like maybe the TAT out in Utah. I do carry tools to remove both wheels, so if I did get a flat I couldn't repair, I could either hitch a ride with a passerby to a bike shop, or a riding buddy could transport the tire someplace for repair or replacement. Naturally, I do carry the tools to repair a puncture, like a string kit and a tire inflator. They've come in handy; I've had to fix three tires in the last couple years (two of mine, one for a riding buddy).
If I was going to carry levers and a spare tube, I think the best place for them is in a tool tube. That way, they're always on the bike, even if you took your panniers off to go bushwhacking. I carry all my tools in a tool tube, including the tire inflator.
I've made several different tubes for different bikes over the years. One example was from a piece of PVC pipe:
Another was made from flat sheets of ABS plastic:
There are a
lot of threads on here on how to make your own, from simple designs to complex ones.