Take your coins offline into a portable SSD once you have a significant amount. Keep it plugged into the power outlet, but disconnect it from your PC. Encrypt the files for a extra layer of security. I'd steer clear of flash drives. I worked tech support and they'd normally die in 1-5 years. SSD can last 80. It will cost you some money to transfer the coins back onto an exchange to sell them, but you'll have nearly perfect security in the meantime.