I typically use 55 gallon plastic drums that have a removable lid. The lid is kept on the barrel by a big metal hoop (I do not have the technical name handy).
Thinking back to old Mr. L&L days. He used drums with the above mentioned hoop. He put his food in the drum which was sealed in Mylar bags. When ready to close he ran a bead of silicone around the lip of the rim then put on the lid and torque down the hoop. Never tried it though.
When burying the drum put a big piece of rock (Blue stone, slate, etc) on top before you refill. I read somewhere that if you use the aforementioned rock, you only need an additional foot of soil on top.
I like Walkers I idea of seeding the soil with nails and another metal bits and pieces.
On another note: I great "cache safe" is PVC piping. You can buy it in 2", 4", 6" etc...All of the way p to 24". Use PVC cement to seal a plug in at one end. Put in the pipe stuff you want too (PLUS a few O2 absorbers) and seal up the other end with PVC cement and a plug.
If your local Home Depot does not have...Lets say a 12" PVC pipe...Go to your local plumbing supply store (Look up in the Yellow Pages).
Burying a long tube might be easier that a 55 gallon drum.
Enjoy