This is very useful to know, thanks. Also, that hack sounds interesting, even tho I am not sure I have the patience to pull that off maybe for a year or two, not sure about years later. But to your point, guess you could just keep letting it grow to pay for a large medical expense years later, and if that never happens just file your old receipts at some point.
I've had an HSA for about 5 years. I've saved $12,000 in receipts from stuff I've paid for out of pocket since starting it... anything FSA eligible like eyeglasses, sunglasses, sunscreen, condoms, my sleep apnea supplies from my DME, doctor visit co-pays, dental fillings, prescriptions, regular STD tests, a TENS machine... etc. Just stuff I was going to buy that insurance doesn't 100% cover, pay out of pocket and save the receipt to reimburse myself later.
So far I have about 175 items listed on a spreadsheet on a new tab in my Excel budget. So I guess the average out-of-pocket is $70, it adds up fast. I have a PDF scan of the receipt, plus a scan of the credit card bill and/or Amazon order or whatever other backup I have of the purchase.
That $12,000 is part of my emergency fund. I know, any time I want, I can cash out that $12,000 with no penalty. Something breaks in the house, something breaks on my car, anything random comes up... that's $12,000 I can have in my hand in 2-3 days.
But I've kept it all invested in stocks and index funds and that $12,000 has grown by about $8500 more inside the tax shelter. Extra return!
BUT, even at the very least.... if you don't feel like going through the trouble of saving receipts digitally for years (don't save paper receipts, those heat-ink CVS receipts go bad in a year),
don't use the HSA debit card to buy anything. Use any rewards credit card you have, even if it's just for a 2% cash back, then reimburse yourself when the bill comes and pay it off with that. That way you get yourself an extra 2% tax-free on top of what you're getting reimbursed for. My $12,000 has generated $240 in cash back, for example, while if I paid with the HSA card it wouldn't have been any extra benefit.