If this is your plan, then its very simple all you need to do is register on an exchange that allows fiat conversion since you want to buy and keep or use peer to peer site such as localbitcoin or paxful where you can get it at a fairly cheaper rate or even use your card in some other reputable sites. After that you then need to move it to a desktop or offline wallet. This is key as you should control over its private key Electrum can be useful here. With that, you are sure nothing would happen to your coins so far your host computer or phone is not compromised. Come next 10 years, your coins is still very much safe.