Medicare Advantage is a Medicare-approved plan from a private company that offers an alternative to Original Medicare for your health and drug coverage. These "bundled" plans include Part A, Part B, and usually Part D.  Plans may offer some extra benefits that Original Medicare doesn't like dental, vision, and hearing.  Each plan has it's own  drug formulary - a list of drugs that are covered.  In addition, drug copays are plan specific.  

A Medicare Supplement Insurance (Medigap) policy, sold by private companies, can help pay some of the health care costs that Original Medicare doesn't cover, like copayments and coinsurance.  Some Medigap policies also offer coverage for services that Original Medicare doesn't cover, like medical care when you travel outside of the U.S.  If you have Original Medicare and you buy a Medigap policy, you may have a Part B deductible.  Medicare will pay its share of approved expenses for covered health care costs. Then your Medigap policy pays its share.

Prescription drug coverage is available to everyone with Medicare. If you decide not to get Medicare drug coverage when you're first eligible, you'll likely pay a late enrollment penalty.  To get Medicare drug coverage, you must join a plan run by an insurance company or other private company approved by Medicare. Each plan can vary in cost and drugs covered.

Medicare is an important part of a health care plan. However, deductibles, co-payments, and other services like dental and vision are some of the costs not included in the coverage available through Medicare. Ancillary insurance is secondary coverage that can help address some of the out-of-pocket financial exposure.