I was on UA2415 yesterday, EWR-PDX, and experienced the same snack box scenario. But I never got an email in advance. Only about half of the pax in F got the email, and it appears that they each had to haggle with GA's for the vouchers. The person sitting next to me was offered a $10 voucher, and after pushing back on how little that would buy in the way of breakfast at OTG outlets, was given $20. The person sitting across from me took the $10 and was steamed after hearing that others got $20.
No proactive use of the hand held devices to issue ETC by the crew, who tried to pin the blame on ground staff. I had to write in to 1K Voice after arriving to get the $100 ETC. And this is what they wrote about the voucher/email/communication snafu:
I'm so sorry you were were not notified of the limited food onboard your flight from Newark. Your email clearly expresses your disappointment. I would like to extend my personal apology for lack of communication to you, and for the additional inconvenience.
We agree accurate communication is essential and can prevent unnecessary obstacles. We will be sure to follow up with our entire staff for a training opportunity to ensure we are doing our best to convey correct and applicable information.
I'm just glad that I liberated a banana from the United Club before heading to the gate. I don't usually do this, but I had a sixth sense that it could come in handy on that flight.