If you are currently donating everything you practically can to charity, fair enough, don't sign up for cryonics.
If you think you should but haven't yet, then sign up for cryonics first. As a person with one foot in the future, you're more likely to do what the future will most benefit from. As someone who avoids thoughtful spending because you feel like you should spend it on charity, you'll end up at XKCD 871.
As a person with one foot in the future
Cryonics only makes the difference between your seeing the future and your not seeing the future if 1) sufficiently high tech eventually gets developed by human-friendly actors, 2) it happens only after you die, 3) cryonics works, 4) nothing else goes wrong or makes cryonics irrelevant. For the median LessWronger, I would put maybe a 10% probability on the first two combined and maybe at most a 50% probability on the last two combined. So maybe at best I'd say something like cryonics gives you two and a half toes in a future where you used to have two toes.
From Mike Darwn's Chronopause, an essay titled "Would You Like Another Plate of This?", discussing people's attitudes to life:
Conclusion, graphs, and references in article. As usual, I recommend reading Chronopause.com as Darwin has many good articles; to quickly link a few: