Copies in multiple physical locations. Copies on paper if it's text. Digital copies on tapes and archive quality DVDs. Storage in low UV, low moisture, low everything fireproofed faraday cages.
Store some complete hardware along with some copies for helping to access the data, along with instructions.
Then assume all of that will fail and take a load of money and put it in a trust so it can be accessed at intervals to your descendents upon instructions in your will where an executor (who is also paid well) can verify that they've done the work to copy your data to the new types of media of the day. Include detailed instructions so that the monetary rewards based off a 1% skim off the growth of the invested funds to increase the chance of the investments lasting through generations. Ensure that the executor can pass being an executor on to future generations through additional financial rewards.
Or just don't worry about it. If it's sentimental data have it live on through stories and good memories :)