Carrying a spare blade is just extra weight you don't need. If you're snapping blades all the time, maybe it's the tool or the technique, not bad luck. Portland prunes are soft and wet anyway, so a bit of rust just helps it slide through the wood. Honestly, finishing the job with whatever is on hand builds character and saves space in the truck. You probably spent more time bragging about your broken blade than if you just grabbed a different saw. Save the backup for something that actually matters, like a flat tire.