Hard to say from the OP what the right balance of effort/cost/risk is here. If it's a bunch of folks at a summer camp or family reunion (where everyone's probably going to have their own copies of the archive anyway), then the risk of losing data is low, even if the capsule archive is corrupted. The shotgun approach of multiple cheap formats, as suggested by others, would probably suffice.
On the other hand, long-term, thermodynamically stable storage requires bulk physics -- engraved/punched metal/paper/plastic, acid-free printing, inert gas environments, etc. Expensive and labor-intensive to create and (probably) also to recover. As a recent article described, it's not for the faint of heart or wallet.
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Hard to say from the OP what the right balance of effort/cost/risk is here. If it's a bunch of folks at a summer camp or family reunion (where everyone's probably going to have their own copies of the archive anyway), then the risk of losing data is low, even if the capsule archive is corrupted. The shotgun approach of multiple cheap formats, as suggested by others, would probably suffice.
On the other hand, long-term, thermodynamically stable storage requires bulk physics -- engraved/punched metal/paper/plastic, acid-free printing, inert gas environments, etc. Expensive and labor-intensive to create and (probably) also to recover. As a recent article described, it's not for the faint of heart or wallet.