bang on about (type 4)

(continue talking about something)

Do stop banging on about your trip to Thailand.

The teacher banged on and on about phrasal verbs.

kick back (type 1)

(rest and relax)

I'm really looking forward to kicking back this weekend. There's nothing that I need to do.

He needs to kick back a bit. He always looks so stressed.

knuckle down (type 1)

(start working hard)

She didn't do much over the summer but she's really knuckled down since September. She's done heaps of work.

Could you please just knuckle down and get your homework done!

stumble across (type 3)

(find by chance)

We wandered round the streets and stumbled across a beautiful little bookshop.

She stumbled across some of her grandmother's jewellery in the cellar.

fizzle out (type 1)

(end slowly and gradually)

Our book group met every month for a year but then it fizzled out.

Our coffee meetings fizzled out a few months ago.