battery with enough power to write on a power failure.
lastFail = lastFail+1 to get how often it looses power
time of write so you know when it failed
and of course lastCount to you have a place to pick up.
in setup, just fill your count value.
as for wear leveling, can you create a new file each day ?
with about 80,000 hours in a day,[ op's seconds a day, thanks wvmarle] you could write once per second and for those bits, stay under the 100,000 mark. and, the benefit is that you would be able to see your daily production over time.