Looking at your question, there's actually a misunderstanding here. Klaviyo does collect arrays of cart items, not just the first item. You can access all items in the cart for your upsell logic.

How to access all cart items

For Checkout Started events (Shopify), you have access to multiple data arrays:

• Items - Simple array of product names
• Line item details within the $extra property with full product information

For Added to Cart events, you get:

• Individual item properties (AddedItemProductName, etc.) for the specific item just added
• Cart-wide arrays like ItemNames, Categories, and Tags for all items currently in cart

Setting up dynamic blocks for multiple items

To reference all items in your flow emails, you'll want to use dynamic blocks with arrays:

1. In your email editor, add a Table block
2. Click Make dynamic
3. For the Row collection, identify your array name:
   • Preview your event data to see available arrays
   • Look for arrays like event.Items or event.extra.line_items
4. Set up your logic to check if each item matches your Regimen criteria

For your specific use case

Your upsell logic can iterate through all cart items to check if the Regimen is present. You'd use the dynamic table feature to loop through all items and apply conditional logic based on product names, SKUs, or tags.

From our experience: Most abandoned cart personalization issues stem from not knowing about the dynamic block functionality rather than data limitations. The cart data is definitely there!

If you're still only seeing the first item, it might be a setup issue with how you're accessing the data rather than a Klaviyo limitation.