Heated walnut oil is food safe (we eat the nuts!) and it is the only
food oil that hardens. Havn't tested it for durability, tho. Vege oils
are not reccomended.
On non-contact kitchen items, like bottle stoppers, I use poly. It's
the only thing I've found that will stand up to the dishwasher, where
everything winds up eventually despite warnings to the contrary.