Avoid affinity cards. Pay cash. Whether it's bad habits or not, I really don't want the feds knowing stuff that's none of their damn business. Another menace...coupons printed from your computer or otherwise tagged with your identity.
Actually, I've kind of gone off the deep end with this....I do buy Chaucer's dog food with a credit card. So on my profile it would seem that I live on dog food!
So they'll know what flavor to give you in detention camp.
Nothing too interesting in my profile -- and I use debit cards normally for which I don't think the same detailed item info is available -- but if I decide to buy some mj next month when the stores open here I'm going to use cash.