I know this was asked over 3 months ago, but the question is still valid and the answer that was given is not.
With CartThrob, a lot of information is stored in the cart_items_info tag that needs to be displayed. In my case, I'm using a conditional whether or not to allow someone to update the quantity in the shopping cart. I'm using Grid to set details about the product and without the ability to parse the Grid data, the conditional doesn't work.
A work-around for most scenarios is to embed a template with
and then using the channel:entries tag in the embedded template to display the Grid data.
CartThrob was updated to 2.5 which added some Grid support but has not fixed the issue with the cart_items_info tag.
Here's the error it's throwing when a Grid field type is within the cartthrob:cart_items_info tag:
A PHP Error was encountered
Message: Undefined index: 106
Line Number: 155
Update - I was able to get my conditional to work by using the embedded template and the entry_id variable, adding the conditional with Grid :total_rows parameter, adding another cartthrob:cart_items_info tag within the conditional and adding the entry_id as a parameter so it will only display a single item as opposed to looping through all items. It's the long way around the situation, but it does fix my problem.
Hoping CartThrob will have full Grid support in the near future.