Is there anything that I cannot ship domestically inside the United States?

In about a month, a friend of mine will be moving back into her parents’ house because her husband is getting deployed to Afghanistan. I want to send a care package to her to cheer her up a bit. I will be sending it from one US address to another US address. I’m guessing I can’t send any weapons and I know I can’t send anything illegal but I don’t know if there’s anything else I won’t be allowed to send.

Do you know of anything that cannot be shipped inside US borders?