Whe it's a regular session, it's quite a good idea to have a couple of songs with "floating" verses sung round the room - eg:

Martin said to his man.
John's gone away on board a man 'o war.

with any luck people will start chucking in new topical verses as well as the standard ones.

I used to go to a club which aways finished with "Wild Mountain Thyme" sung around. I would try and concoct a new verse every week, so that I wouldn't be stuck when it came to my turn. I would often find that my previous "additions" would have been noted and trotted out by someone else before it got to me. One which I can remember (we had a couple of welshmen in the group) was

If my true-love chucks me out,
Then her love she can keep.
I'll just pull on my wellies,
And find myself a sheep.