Save your receipts and have your HSA cut you a check later in the year.
This is what I do even though I have plenty in my HSA. I pay with a credit card (more rewards) or cash/check (sometimes the dentist gives me a 5% cash discount!) and submit the receipts to the HSA.
There is a backdoor sort of way to use the HSA.
Example:
Year 1 you have a HDHP, open a HSA, contribute $3350, and have $3000 worth of qualified medical expenses for which you withdraw $3000 from your HSA. Ending balance $350
Year 2 you have a PPO and no HSA or FSA. You have $2000 in medical expenses that qualify for HSA withdrawals. You withdraw $250 from your HSA and save the receipts for $1750. Ending balance $100 to keep your HSA account open
Year 3 you have no healthcare coverage and have healthcare expenses of $250 for which you save the receipts from. Your HSA is still open with $100 in it
Year 4 you have a HDHP, contribute $3350 to your HSA that you opened in Year 1. You can now submit your Year 2 unrefunded receipts for $1750 and Year 3 unrefunded receipts for $250 to your HSA and get reimbursed for them.
Now this will only work if you keep your HSA open. They keep track of the open date and any receipt dated after that is valid for reimbursement as long as the funds are available.
There is also retirement benefits available via the HSA talked about here:
http://blogs.reuters.com/shaneferro/2013/07/18/hsas-when-your-health-insurance-becomes-a-retirement-account/ Oddly enough my HSA has cheaper and, in my oppinion better investment oppertunities than my 401k.
Eventually, after I pay off all of my student loans I will retain the receipts as another layer of emergency funds and submit them when I need the money or for my post retirement but pre-59.5 years.
Hope this helps you!