Peter Cade | Photodisc | Getty ImagesAs open enrollment arrives, millions of Americans face key decisions, such as picking health insurance. If the plan comes with access to health savings account, or HSA, contributions, you could use the funds for long-term investments, experts say.    While most workers spend HSA money on yearly out-of-pocket health expenses, a small percentage invests the balance, which can grow tax-free for future medical costs.      "The plan is to go into retirement with a six-figure ...