Can a shopper have buy now items and TryNow items in one cart?

Yes, by default this is feasible and natively compatible with Shopify checkout. This is referred to as a Mixed Cart.

Checkout Example

A shopper's cart will look like the following in checkout:

• Shopify automatically sums the buy now item values to the Due today amount (in this case the Core Sweatshort)
• Shopify automatically sums the Try Before You Buy item values to the Amount if kept
• Only the TryNow items will display the Try Before You Buy selling plan at the line item level

Shopify Order Details

TryNow will charge for the buy now portion of the order and authorize for the TryNow portion. As such, the shopper is likely to see multiple transactions on their credit card statement: a charge and an active authorization.