How to teach my 20 week old Golden puppy to leave things when walking

[ThierryHenryismyBoyfriend]

Title says it all. We have a beautiful if somewhat dim golden retriever who is becoming a big boy (I reckon he'll be the size of a shetland pony when he finishes growing!) and when he's out for walks he does ok until he sees:
a blade of grass fly past his nose
a crisp packet
a sweet packet
empty drink container
a person (with or without a dog!)

Hopefully you get the picture. Any top tips to get him to 'behave' and ignore these little distractions?

[Lizcat]

A very gentle tug on the lead combined with the words leave it. Mobile mop only 15 months old managed to leave a dead chinese takeaway the other day after training him with leave it.

[ThierryHenryismyBoyfriend]

I'll give that a try thanks Lizcat.