I read somewhere that the average metropolitan hospital only has on the order of 150-300 body bags on hand. Why that number? It's what would be handy in case of a plane crash. In terms of pandemics---and unless something has changed in the past few years which is probably doubtful---the US is rather unprepared($). The total number of people who can be treated simultaneously for something like Ebola in the US is about 10ish(*) insofar all procedures are followed and the proper hightech equipment is used. The key-resource on this is Michael Osterholm at CIDRAP. He's written a bunch of books for mainstream consumption as well.
(*) If you ever catch Ebola (ha!), you'll definitely want to be in one of those units ASAP.
($) The idea of paying to maintain excess capacity in case of a rare event goes rather against the mantra of health care profit maximization and individual freedom of choice. For starters, it would cost a lot of money ...
This of course pertains to what happens AFTER people get infected. The primary defense is to avoid getting infected. This means avoiding vectors. Very common vectors are other [sick] humans. This means achieving herd immunity for vaccinations and if nothing else then definitely be vaccinated oneself. Unfortunately, there's an increasing number of yahoos (first progressive Luddites on the left who believe in getting sick naturally or something ... and now low-educated far-righters who avoid modern medicine in the name of freedom) choosing not to be vaccinated. Well, in general, having the disease rarely if ever makes you stronger although it does in some cases make you immune. IOW, the idea that "as long as it doesn't kill you ..." is misguided. Preferably you'd always want to avoid the disease. Unfortunately, it seems the social maturity is not there. If no vaccination is possible, it means eliminating the vectors. This can be as simple as proper sanitation. This, in fact, is a big reason why cities are no longer the death traps they once were. But if your city is demonstrating an inability to keep sewage from flowing in the streets (e.g. during extreme rainfalls) it's time to leave. Here I'm mainly thinking major cities with sewerage systems inadequate for the combination of extreme weather + increased population, but also see comment about LA below.
On the personal level ... don't touch your face. Wash your hands frequently. Don't inhale other people's exhalations. Wearing a mask is dorky but it works. Do all that, and you'll probably be one of the last people to catch it
Other vectors are harder to stop, e.g. mosquitoes and ticks. Still, window screens has done wonders (malaria used to be endemic on the entire eastern seabord prior to screening residential buildings and draining most/all of the swampland. Ticks are on the increase practically all over the US now. This is because of humans constructing homes in "natural surroundings". This, in turn, means eliminating predators (gotta keep people safe) which causes a runaway of the carriers (deer, mice) that the ticks feast on. Much of this can be avoided by staying away from nature. Yes, I realize that this is now a choice between getting infected in the city or in the countryside, but there are simply too many humans around or rather too little nature left.
Staying overall healthy is a good move. Aside from barnyards being zoonotic breeding grounds, another source, not mentioned that often ... are older folks on immune-suppressant drugs (lots of drugs will do that as a side-effect, so check into it). Yeah, fun stuff ... if you're one of those who had measles because you weren't vaccinated, whether intentionally or because it just wasn't available at the time, taking one of those drugs could lead to shingles. Whereas if you were smart enough to be vaccinated ...
General antibiotic resistance is a professional problem. Hard to say what individuals can do about it. It's a tragedy of the commons problem perhaps best attacked at the regulatory level whether professional orgs or government. Incidentally, the first case of a superbug resistant to the entire battery of US antibiotics happened a few years ago. People already die from this ... but not en masse. It's mostly MRSA stuff ... I think this was discussed in a previous thread around here.
Basically, like with oil, we've enjoyed a couple of generations of massive prosperity thanks to largely eliminating diseases and food and energy shortages. And then we'll go back to normal ... Point being, "health" will probably have to be somewhat redefined at some point lest there be some massive evolution in the social dimension either morally (voluntarily) or regulatory. For example, the Soviets did reasonably well until things collapsed.. then it was all tuberculosis and HIV from there.
It might surprise you to know that there are now regular cases of typhus in Los Angeles these days... or that hookworm is rather widespread in the poorer areas of the deep south once again (about 10M+ Americans infected).