What digital assets can you put in an NFT?

I was wondering what different digital assets you can link to an NFT. Like for example below:

{
    "attributes" : [ {
      "trait_type" : "Token",
      "value" : "Bitcoin"
    }, {
      "trait_type" : "Test type",
      "value" : "Test value"
    } ],
    "description" : "Test pic of BTC.",
    "image" : "https://gateway.pinata.cloud/ipfs/QmZPiFSiqZyZbK74DoSpNpEQ1CcGenGn35y8JzpcAagXBn",
    "name" : "Bitcoin Pic"
}

What other assets besides “image” can I use? Like right now, I can view the minted NFT through metamask and the image shows up properly, so what other assets would function correctly in this manner?