I heard of a guy that was 6 months ahead. He did not take any
controlled substances, so I do not think this it was illegal.

Think creatively.
Generally, every time something changes, you can get a few
days to a few weeks ahead. Any of these changes, offer
opportunities for you to get ahead: change Pharmacies,
change prescriptions, change doctors.

If you keep close track, you can keep getting
your meds at 24 days (or whatever) so you are
progressively farther ahead each month ( each 24 days).

If you tell your pharmacist that you are going on
vacation, he can probably get the Insurance Co to
authorize an early purchase. Then, most likely,
24 days later you can fill again. You might get
away with 2 vacations a year.

Most insurance companies (did) like you to order 3 months
supply through the mail. Saves them and you money.
To your advantage, get a written prescription for this,
and send it in right away. But, you still need to fill
locally, because the mail could take a long time, right?

When you get a new prescription, fill it immediately,
but take the old meds till they run out. Of course,
you must use good judgment on this one.

To save money and give you flexibility, ask your doctor
to prescribe generics. Sometimes generics are so cheap
that you need not buy them using your insurance.

Some people get a full year, written prescription, for
every drug, with generics enabled. It can save hassle,
but does not really help your question, directly.

Some discounted drugs are so cheap that you do not need
the Insurance Company. See below on Costco, Target, etc.

Lately Costco offered good deep discounts for 100-days worth
on some drugs. It might be good to get 100-day option enabled
on your written prescription. I would think that Insurance
companies would like this, but no matter, they are real cheap.
You dont have to join Costco, to use their pharmacy;
have some cash, no Credit Cards(?), no checks(?).

Wall-mart and Target give dirt cheap prices, on some drugs,
so you do not need the insurance company.

Whenever your doctor changes your prescription,
ask for some short term Samples, but fill the written
prescription immediately; this puts you ahead.