What is the alternative solution since getCart is deprecated?

I have scripts running in the SuiteCommerce user's browser that need to see what the subtotal is on each page of the checkout, so that it can overwrite the Total displayed on the screen after adding the full truckload freight cost (something we had to do ourselves in a suitelet because NetSuite doesn't support freight that isn't a parcel service as far as I know). The total is the subtotal + the calculated full truckload freight cost.

Every call to getCart throws a warning: "getCart() is deprecated!" but there is no documentation I can find on what to use instead.

I have tried using SC.ENVIRONMENT.CART, but this does not update reliably, whereas, getCart does. I cannot use an unreliable variable or many customers will be told the wrong amount, different from what they end up with when the same calculation showing the predicted price is applied in the scriptable cart UserEvent script on beforeSubmit, to add the freight cost as another line item (that part works fine).