Do they have to be specific to the particular place you're applying for?

And what should they say, all I can think of is your availability to work (for a part time job) and sort of why you want to work there, but that's a pretty tough one.

I've had three shifts in my new job and I'm fed up with it already. I need a new one and as quick as possible because I'm skint, skint skint. I was thinking of just printing out hundreds of CVs and handing them in everywhere I can think of. I've already got a CV, but I don't know where to start with a cover letter.