I've written about this subject substantially a number of times here, so I'll just summarize.
Antibiotics can be life savers, absolutely, but their safe use depends on knowing the infective organism (they are worse than worthless against any virus) and not just any antibiotic will kill any particular bacteria... so for the most safe and effective use, a laboratory is required to match the germ with the medication. Much of the "superbug" problem, resistant bacteria, is the result of skipping this necessary step, irresponsible and casual use of the most powerful antibiotics for ordinary infections, and failure of patients to take the medication for the full course. Consequently, there are an increasing number of bacteria no longer responding and are more life threatening than ever.
Oral antibiotics are not nearly as effective as those given IV, so it is important not to expect one to replace the other. And no, it is not a good idea to accumulate IV equipment and supplies for post SHTF use because you will not have a sterile environment to make or mix the solutions, and they do not have a long shelf life even in powder form. IV medication requires professional evaluation and observation because side effects can be serious and even deadly, very quickly. An epi-pen isn't going to cut it.
In addition, many antibiotics are made with fluoride.
http://www.nccn.net/~wwithin/fluoride.htm Index of Fluorinated Pharmaceuticals
"fluorinated antibiotics Floxin, Levaquin, and Cipro can cause nightmares, psychotic reactions, paranoia, agitation, manic reactions, aggression and hostility, hallucinations, and even depersonalization, all symptoms associated with acts of homicide and suicide."
"In 1990, about 220 fluorinated pharmaceutical drugs were on the market. Now some 1,500 are under development."
Many Antibiotics, Anesthetics (general), Anti-fungal antibiotics, Appetite suppressants, Antacids, Antihistamines, Arthritis (rheumatoid), Anti-anxiety, Antilipemics (cholesterol lowering), Psychotropic (anti-psychotic), Antibiotics (Fluoroquinolones), Anti-malarial, Steroids/anti-inflammatory agents, Antidepressants, Antimetabolites (chemotherapy).
Antibiotics will assist a good immune system, but it will not be much help for someone with a very poor one. Keeping your immune system healthy would, then, seem like a logical priority in any case. Optimal nutrition, hygiene, avoiding obvious sources of infection where possible, and adequate rest is essential. No antibiotic can replace any of those things.
So, do your homework, know what you are getting and how to use it. And pray you never need to even consider it.