A lot of so called “subsidies” aren’t direct cash payments to big business, but are instead things like preferable legal status, tax benefits, favorable access to natural resources and so on. Because of this, it’s not clear what you mean by “left to the free market”, because there’s not necessarily any baseline to roll things back to. Nonetheless, I’ll give it a shot.
Life would, more or less, go on as usual. College would get a lot more expensive for most people since government subsidies would be gone, but it still exist as it previously did.
Oil companies deal largely with land leased from the government–assuming this doesn’t change, they would probably become less profitable as they lose favorable tax treatment, and more profitable as they become free from regulatory burden. My guess is that prices wouldn’t change drastically, especially since major oil corporations are multinational and thus would be largely unaffected by this change.
Energy companies would become drastically more profitable as they raise their rates significantly to take advantage of their monopoly status. People would almost certainly pay substantially hire electricity rates.
Road construction and maintenance would fall off entirely because roads are built by private contractors paid by the government. A handful of private highways exist, and more could be built. However, it’s unclear how a privately owned network of roads could be maintained.
Corn farmers would become less profitable with the loss of government subsidies, and especially due to the end of the ethanol mandate. This would be tempered by a reduction in regulatory costs, but I would guess corn farming would become a whole lot less profitable.
FDIC insurance is a negligible part of the government’s involvement in the banking system. Far more significant, if we are moving to an entirely free market, is the end of the Federal Reserve and the end of the extensive regulatory regime that heavily manages the banking sector. The extent of government regulation really is enormous–you’ve got the SEC, prohibitions on insider trading, required reserve rations, and much more. You could reasonably expect more bank failures, many more banking runs, and shorter, more extreme, and more frequent economic cycles. Libertarians have some idea about how a privately owned “clearinghouse” could replace the role of a central bank, but that’s fairly speculative and would take time to be implemented if at all.