Here are some tips that I've learned the hard way over the years:

Place bottled water in the bottom of your cache. If the bottles leak nothing else will get wet.

Never store leather articles in a cache that is air tight. Leather will dry out and become un-useable.

Store batteries separate form their devices(lasers, radio's and GPS).

Pack as much as possible in vacuum sealed bags.

Last thing in the cache should be a small daypack, just so you can carry everything away quickly.

Keep the location secret!!!!! Reading Yankee Canuck's post above QUOTE' " I know a man who says he keeps a survival kit in his wife's flower bed."

He better not count on it being there when he needs it!