You want to check out the History channel's series "Life After People," which digs into what would happen if suddenly people did not exist. They go in depth, showing what becomes of farmlands and farm animals, roads, buildings, cities, different kinds of structures, ships, the oceans, lakes, and rivers, wildlife, domesticated animals, everything you can imagine. It's fascinating.
What survives depends on multiple factors. What happened on the surface that forced the survivors to shelter in bunkers? What was the nature of its damage and how widespread was it? How many survivors is "few"? How remote is the part of Texas s/he's in? What determines the route to Florida? Are there survivors preying on others? Does your character have the ability to ride a bike? How well equipped is s/he? Can the character carry water and food enough to last for days?
I would expect that the more isolated an area was back before whatever happened happened, the more might survive. Crops, for instance, will come to seed and re-sow naturally for many generations, while weeds and critters are not controlled by intact fences and pesticides. So your character might find something to eat as it is (leafy greens, corn, fruit, soy and other beans), something that needs processing (think wheat), or only cotton. Some buildings will be standing, others fallen, especially as he nears the coasts impacted by hurricanes.
Food in cans may be safe to eat if it was stored in a basement where it never got hot. Dried foods and food in glass should be okay. Wells will be there, although the buckets and pulleys will have broken down.
Are you in the point of view of an American character in Texas? S/He won't use terms like "traincars" or "shops," so you want to be careful on that sort of thing.