Automatic Reordering items in the Cart. Read the case

Question

Case:

I have a feature in my eCommerce website where I run bundle-offers (example: Buy 1 get 1 free, Buy any 2 shirts of Brand X and get 20% off on paid price)

User Journey:

1. User goes to the product details page of a shirt (SKU code: S1) (of Brand B1)
2. User sees an offer associated with this item. Lets say the offer is "Buy any 2 shirts of Brand B1 and get 20% off on paid price"
3. User adds S1 to cart
4. User goes to the product details page of a jeans (SKU code: J1) (of Brand B2). There is no offer running on this item. User adds this item (J1) to cart.
5. User goes to the product details page of another shirt (SKU code: S2) (of Brand B1) and adds it to cart

Situation:

Now, in the cart we have 3 items listed in the following order (top-to-bottom): S2, J1, S1. I want to automatically change the listing-order the items in the cart to this: S2, S1, J1 - Because I want to group the bundle-items together and show a congratulations message to user, telling him that he just got an additional 20% off on the 2 items that he is buying together.

Question:

Should I auto-reorder the items or not? If yes, then, every time the user will add an item (like S2) that is part of an offer (similar to above) and while he had already added another item (like S1) in the cart some minutes before, the items in the cart will be re-ordered. This situation will worsen in cases when multiple offers would be running on my website, every time the user would add an item (on which the running offers are applicable) in the cart, the order of items in the cart would change.

Answer 1

I'd say no, the bundling of the items can be shown on the receipt, you should keep the cart ordered top to bottom, that way your user doesn't get confused and think they haven't added an item when they did because they expect to see it at the bottom but you've re-ordered it to some other place.