Here are some sevaras I'm thinking, although again, haven't really looked into this and many here have probably thought about it more than me.
1. CB, points on generic spend, seem akin to a rebate, which means you just paid less for the potatoes you were buying. Hard to see that as taxable.
2. Same with FF miles you get for flying. You just paid less for your flight.
3. IRS Announcement 2002-18 was about business travel. Your employer pays for your flight, and you get miles. If was like scenario 2, the employer would get the miles. So this is more like your employer giving you additional compensation in miles, but IRS was mochel it.
4. Points or miles you get from deposit bank accounts, seem most like interest income. Hard to see it as anything different.
5. MS from buying groups. If you treat it as having paid less for potatoes, like under scenario 1, then your basis in the potatoes is less, and you had a profit when you onsold it to the buying club guy. So seems like either business income or short term gains (with various nafka minas).
6. MS from GCs. This is the weirdest one, because it seems irrational to say that your basis in a $500 GC is only $492. However, I can get past that weirdness, especially considering that you can trade GS below face value all over ebay. So hagah atzmecha: If I buy a Target GC for $475, and then buy $500 worth of potatoes at Target, do I have income or gains of $25? That seems like an insane position to take. But that's where the usual theories would seem to take us. If you have a business, I would think very hard to argue that the money you are making wasn't made. But seems nuts that you have income everytime you buy a GC below face value and then use it. At some point it may just come down to the optics.
These are just some boich sevaras--no idea how IRS thinks of this or what law is.