It depends on how long the stuff is expected to stay in storage and who is supposed to use it. If it's just being stored for a few centuries I don't think you can beat just storing it in some stable orbit in the shadow of some planet after removing any charge from batteries and such. Intense, unchanging cold is the way to go to let stuff keep for long periods of time.
It's easier to access than putting in the Oort Could and can be monitored against theft much easier.
Failing that, store it at the bottom of the ocean. Again, it's very cold down there, the conditions don't change and covered with the proper sediments and such the environment will be quite oxygen-free.
At the other extreme, I had a group of PCs who were going to swindle the Beedling Society (mentioned in "Survival Margin") in an MT game. However, in the process of getting the funds, they came to believe in the Society's cause and instead started using their own money to set up their own caches. They had some pretty creative ideas for storing devices and methods to recivilize humanty after a Long Night - though the most successful of the caches turned out to be the one that created "Batman" on a TED controlled world.