I've never quite got the hang of what I'm supposed to say at A/G fields - I use them so rarely and they all seem to be different.
The most recent one I took off from, they told me at the desk to book out on the radio. So I called
"xx radio, G-ABCD, taxi for VFR flight to yyyy, three on board"
roughly as I would at an ATC field and got
"G-ABCD, runway in use xx, QNH yyyy"
which worked fine.