[El Sordo]

An additional suggestion for all:

Twice a year (pick two days... first day of Spring and first day of Fall, General Conference, whatever...) bring the kit out and unpack it.
-Spread the items out so you can take notice of what you have in there.
-Inspect each item.
-Replace anything damaged or expired.
-Make sure the spare clothing still fits.
-Add or upgrade items with respect to how your family needs may have changed.
-Then properly re-pack it.

This makes for an excellent opportunity to not only keep aware of what you have in the kit as well as keeping the thing properly stocked, but also to avoid ugly surprises like:
"Honey, where are the radio batteries?"
"Oh, I took them out last year when we gave little Johnny that walking robot for his birthday... I've been meaning to buy some more..."

[Utah Girl]

Good idea. I usually go through my kit during October's General conference, once a year. Since I live alone, I figure that I should be OK doing that. I used to go through twice a year, but now just once...