Our auto club is a part of a group that have arrangements with AAA. What kind of benefits can we expect?

Can you tell me about campgrounds in national parks? Do they have showers (at least in bigger parks like Yosemite)?

My friend said he wants to buy a t-shirt from every state we'll visit. I assume they sell stuff like this in visitor centers. Is it sensible to buy memorabilia in visitor centers or are they massively overpriced?