You can list as many donations per charity as you like. After you add a charity and a non-cash donation, there is a button at the bottom of the screen for "add another donation."
You need to break up your donations by charity and date, but within a specific date, you don't need to list every specific item. You can group them together, there is a drop down menu with "used clothing and household goods" as an option, and then on the next page you can add additional details.
You are required to have your own written inventory listing the items with enough detail to determine their fair market value--at a minimum, a brief description and condition -- (good or fair; poor is not allowed unless you have a signed appraisal). You do not need to post every item, you can group them together, as long as your have your inventory to show the IRS in case of audit.