So:

I'm graduating college in Pittsburgh in May. I'm starting work in San Diego in August. I want to spend the summer going cross-country. Immediately out of college, I obviously won't have a lot of money to throw around, though I am putting in some work this summer and should be able to bring in something over a thousand dollars, plus I'll be selling several of the used bikes I've accumulated during college. If worst comes to worst, I can borrow from my parents, but I'd prefer to avoid that, and thus want to keep costs minimal.

I'm a pretty decent self-taught mechanic and have access to my local bike coop, which makes for a pretty decent selection of random used parts, though most useful commuter-type equipment disappears pretty quickly.

There's a lot of equipment that seems to be de rigueur for taking a trip of this length. None of the bikes I have now are to be too suitable for the trip. I'm watching the coop and Craiglist for suitably-sized old mountain bikes as well as keeping an eye on eBay. But where are likely points of failure where it's worth my while to spend money on new things?

What about other equipment, like racks and panniers? How much of a risk would be using cheaper Axiom racks or such versus shiny handmade European things? What about panniers? Do more expensive ones just offer the convenience of easier-to-use connections and being able to keep things dry without garbage bags?

Then there are tents and equipment in that direction. I don't know much about those. It sounds like any basic tent will do the trick in the summer, and that a pop-can stove will do fine. Is that true?

ACA maps are also nontrivially expensive. Are they worth it? I should have access to an Android phone this summer, and thus will have access to Google maps and even without internet can keep a copy of OpenStreetMap data (which would probably be mostly US Census TIGER data in the countryside).

Basically, where is it that buying pricy things means avoiding getting stuck or soaked in the middle of nowhere, and where does it just make things a little more convenient?