I admit – I get a guilty feeling when I share this one. Health Care FSA has this interesting feature – it reimburses you for your medical expenses even with money that you have not yet funded into your FSA.

See here: https://www.fsafeds.com/support/faq/all/1003 
“If you used your entire elected amount before FSAFEDS has deducted it from your pay, you will not be responsible for the remaining allotments.” 

For example: 
You enroll in FSA and plan to contribute $2,750 incrementally over the course of the year. If you incur a $2,750 expense early in the year, FSA will reimburse you the entire $2,750 even though you haven’t contributed $2,750 yet! They have fronted you the money, assuming they will collect it incrementally over the year. But if you leave before the end of the year, you will not be required to pay back the money the fronted you.   

So, in theory, if you are planning to retire in January, you could opt during open season to participate the maximum into the FSA, then schedule any medical, dental, or vision, work that you want for January, and FSA will front you the amount of your FSA participation.  Thus, you can get $2,750 (minus one pay-period) of free money from FSA! 

Stephen