Classic New Zealand slang that means; To have a go on something.
Also a sandwich.
"Giz a blat on your missus ow"
- May I partake in courtship of your acquaintance
"I went for a blat in my bro's RX-7 and it was mean"
- I drove my friends rotary sports coupe until it broke
"Nah, he's a fucking stally cunt - He wouldn't even give me a blat on his pie"
- Social complaint about someone not sharing their mince and cheese meat pie.