Buying One Item With 2 Cards

The 800 points were with the card? Usually if you purchase a card that has 2 items with it, there are 2 codes to redeem: one of the points and one for the subscription.

Game pass cards are not gift cards. So no, you'll need an Xbox Gift card to buy in game items.

They're consumable items, no one should have to be told that you can't share an item sold as a microtransaction. If you bought a $50 Xbox card would you expect to get one for each console? They already let you share games and dlc with the home console feature.
I just don't get what your complaint is, "Give me free doubles of in game items"? No one is forcing you to buy 2 req bundles, in fact you can only buy 1 per account, but who ever actually purchases the bundle is the one to get the packs.

Also the actual cards you get from the req bundle is not downloaded to your xbox, just your right to open 2 free packs of random cards per week. If you were to get banned from Xbox live those remaining packs would be forfeited, where as an actual dlc which
is bound to your xbox can be played even when your account is inactive (as long as it's downloaded at the time of restriction). If they did what you suggest they should people would just bounce gamertags and no one would buy the bundle, just piggyback off
of others.

I think if you buy stuff for the Xbox 360 from the store online, it asks you to add payment, if its Xbox One, it doesn't ask. Also you can just add a credit card, buy your item, then delete that credit card off as payment

In my answer I included the credit card as method of payment and the prepaid currency cards (yes these are the gift cards) and I already stated that you can purchase (purchase as in buy for a price) avatar items through your xbox 360 and use them in your
xbox one as well.

To get the free avatar items (as in giveaways or items) you don't need a method of payment in your xbox 360.

Hope the matter is clear to you now!