Can I combine withholdings together for box 14?

Yes. Although box 14 only has room for 3 items, you may choose to combine withholdings together. For example, if you had 2 items that were both health care related, and wanted to add them together to appear on one line in box 14, you would enter the same description of HEALTH for both of them when you Map the withholdings (image below). See: Using W2 Software and Can I have more than 3 items in box 14?