Buy with CASH whenever you can you can pretty much assume that anything you buy with paperwork credit cards,etc. will be known and will have you tagged.
Buy in disparate places don't buy all your supplies in the same place, sad to say but it's looking like even buying non-perishable food is becoming ‘UN-PC’ as it were.
Keep quiet about it, don't advertise what you are doing.
By the same token (yes, I'm going to contradict myself) encourage others that you can trust to also prepare, you don't have to blab to others just what you have, but it would be a very good idea to get like minded people to also prepare.
I did. I'm happy as a clam. ;-)