Remember that your back-up cannister only needs to be one of those little 100gm (net) Jetboil jobs. It could be one of those things one carries for the few, as with a comprehensive Medi-kit, PLB etc.
I've gotten 10 days twice, out of my larger cannisters and I cook porridge, but i'm very careful with wastage nonetheless.
The old, thicker Trangia bowls hold their heat better than the new thinner ones. (101 vs 78 gms each).