Medical spending includes expenses for hearing, vision and dental health, even if you don't have insurance for those! So, if you're due for a teeth cleaning or eye exam, make an appointment and you can use your FSA to pay for those visits, including copays and coinsurance.
You can spend your FSA money on medical expenses for you, your spouse, children or any other qualifying dependent you claim on your taxes. If you have grown children on your health insurance plan but don't claim them as dependents, you can still spend FSA money on their medical expenses as long as they're under the age of 26!
If your needs change from year to year, then plan conservatively. If you know you have a lot of expenses coming up, then consider maxing out your account.