mmmm, good thread!
Batting lower order for the first half of my adult career, i only every had one bat. Not only that, but i only bought grade 2 willow! Couldn't justify the price for something that would only get used for a handful of deliveries before change of innings (i broke the club record for most "not out's" one season).
Since i did a trip to India a few years ago with work and picked up two bats cheap, i've always carried two bats to every game. One is always the main bat and the other, just in case... Wet pitch, change in the weather, or, god forbid, the main bat breaking... are the only reasons.
Bats always a few seasons apart.