Yesterday, people were scrambling for them. Today? There's no market for solar eclipse glasses--
There's a sale on eclipse glasses today.— Beachbum (@Luvs_Summer_) August 22, 2017
We joked about holding onto your eclipse glasses because there's another one coming up in 7 years... and were quickly told that the glasses have a 3 year expiration date and would not be good.
Then we heard from NASA that's not necessarily the case--
"Note: If your eclipse glasses or viewers are compliant with the ISO 12312-2 safety standard, you may look at the uneclipsed or partially eclipsed Sun through them for as long as you wish. Furthermore, if the filters aren't scratched, punctured, or torn, you may reuse them indefinitely. Some glasses/viewers are printed with warnings stating that you shouldn't look through them for more than 3 minutes at a time and that you should discard them if they are more than 3 years old. Such warnings are outdated and do not apply to eclipse viewers compliant with the ISO 12312-2 standard adopted in 2015. To make sure you get (or got) your eclipse glasses/viewers from a supplier of ISO-compliant products, see the American Astronomical Society (AAS) Reputable Vendors of Solar Filters & Viewers (link is external) page."
So you CAN keep them and reuse them, if they're compliant... and they don't get damaged.
But if you're not sure you can remember where you put your eclipse glasses 7 years from now, or you're worried they might get scratched or damaged, why not donate them? There's another eclipse in 2 years, and schools in South America and Asia would love to have them--
And here are a few other options--
Me? I'm keeping mine as a souvenir of something fun I shared with my co-workers.. one of the few times we were on the roof together!