Besides everything everyone else said, keep a book of your friends, and how to contact them. Then as often as you can, reach out to them. Even just a text like "Hey, how's life" is good to keep a friendship going.
And keep a copy of your own health records. You don't need to see the doctor's files, but you should know dates when different tests are done, and the results. A paper notebook is best, but I just email my wife with the subject "HEALTH:"