If you want data then you need to go on the USA Extreme Plan or the USA Max Plan as these are the only plans with data. You can't add data packs to any of the other plans.
The USA Extreme Plan and the USA Max Plan last for 30 days. You can't pay just for a week or two - you need to pay for the full 30 days.
If you don't want data then you might want to consider one of the other cheaper plans (USA Saver, USA Daily or USA Budget) but they do NOT include any data and you can't add data packs to those plans.
Click here to read about the available phone plans.