There are two main reasons why you’d want to set up a cache or two. First, it is to hide items you want reasonably accessible but not in the home. For example, you have a few firearms you want to keep out of reach of young children. The second reason is to set up locations where you can resupply yourself if you’re on the move, such as during a bug out.
Caches are a great idea, if they are located properly.
If you’re out in a rural area, setting up a cache can be as easy as digging a hole. As long as you’re off the beaten path, the odds of someone stumbling across it even with a metal detector are fairly remote. Caching in an urban area though requires some creative thinking. It can be more difficult than rural caching in that there is a higher degree of risk of you either being seen planting the cache or that someone else may happen across it.
One suggestion would be to install a fake utility box on the outside of a building and use it for a cache. Add a padlock and your stuff should be reasonably safe.
If you work in an office environment, what about stashing some stuff in the drop ceiling of the bathroom?
Burying caches at a public park is possible but probably illegal, keep that in mind.
If you’re looking to keep the cache closer to home, you could bury it under your rain barrel or even your sidewalk.
Urban caching may be a bit more difficult but it certainly isn’t impossible.