PLEASE be wary of fake alerts showing up as emails "from" PayPal, Amazon, banks, etc; as Facebook, text and WhatsApp messages; and even as phone calls with spoofed caller IDs (notably one that says Con Ed is calling). Advice here about what to do if you receive a suspect message; and hoax-slayer.net is one good site for learning more.
Preparing a bunch of cash tips? Save time: figure out how many bills of each denomination you'll need with our Holiday Tip Calculator. (Also available here as a Google Sheet).
Have expiring airline points? If they're not enough to do anything else with, you may be able to trade them at Points.com for Amazon and other gift certificates. You won't get much value this way--but better than nothing. Detailed analysis here.
And as you snap a bazillion pictures of family, friends, and holiday windows, check out this excellent NY Times guideto sharing photos online.