[INJ} I am given to understand by today's youth that "to bail" would indicate giving up in a dramatic way. It would appear to come from "bailing out (of an aeroplane)". Incidentally, "Keep Calm and Carry On" is available on a mug in my own kitchen.
[Kagome...] If you have a lst of things to be done (from the latin gerundive), or an agenda, and it only contains one item, it is still a list of things to be done. So I disagree, and would say that an agenda for a meeting is always an agenda, regardless of how many items are on it. More specifically, each item on an agenda would be an agendum.
[Phil] I have a "Keep Calm and Carry On" t-shirt. frogstar has one that says "Now Panic and Freak Out". To date I don't think we've worn them at the same time.
[KS] A datum is a data point and so is a count noun with a plural of data. However data meaning information is a mass noun and takes a singular agreement.
The whole 'Just Bail' Idea related to something one of the guys I know from my accommodation, who once said 'let's just bail' at a party, and so it stuck, and got written on a large board and put in the window. It was then at a recent poster sale that we saw a 'keep calm' poster, and decided to change it. It was initially going to be 'Just Bail', but this would not fit with the whole idea of an odd number of lines, so the expletive got added. We are now planning on getting the poster printed up at A2 or A1 size, and put on the kitchen wall.