Congrats on getting out!
You will want to leave the "sweats" and "sweatshirt" behind. You don't want cotton at all. It will not dry when it gets wet and can lead to hypothermia. If you don't have synthetics you can get some from Walmart or somewhere like TJ Maxx. The difference between the "cheap" stuff and the "good" stuff is in the details. The cheaper shirts not designed for backpacking will often have seams on the shoulders where your pack sits. For some folks this is not a problem, for some it is.
Like others have said, for your first trip it would be easier to do the commercial, dehydrated meals. Mountain House and Backpacker Pantry are common in outdoor stores. I have used some Enteria makes some good stuff but it is not common in stores. My favorite is
Packit Gourmet but they only sell online. You can probably get some Coleman brand food from Walmart (you can here).