If it happens in 3 months to 50 snakes, or even 5, you are clearly doing something wrong.
Antibiotics are toxic - improper dosing can cause longterm problems (and/or death). Heck, for that matter, so can "textbook" dosing if the animal is already dehydrated. There are numerous considerations, possibly even some legal issues.....again, it does happen sometimes, but it is usually based on a level of comfort. If the vet knows you, and is comfortable with your knowledge and judgement, he/she might go along with it. By the same token, unless you have ongoing or frequent issues, or animals with known health problems that require it, why would you need antibiotics on hand? Using them when they aren't "needed" (let's be honest, RI is an incredibly overused term in this hobby...first symptoms are generally indications of husbandry problems, not actual infection) can lead to resistance; and there are different antibiotics for different things - use the wrong one, and you stress the animal without fixing the problem.
It can be a nice thing to have - don't get me wrong - but what happens when you go 8 months without a problem, and you notice that the drug is past the expiration date (or, worse, is discolored)? Do you have syringes and needles for administration? (you do know those shouldn't be thrown in the garbage, right?)
Basically, all I'm doing is pointing out things you should already have considered...I'm not trying to talk you out of it, or to be negative about the idea. Hope your snake recovers quickly.