Hi sj

That's a really hard question to answer without knowing anything about your dad's friend. It set me looking through mudcat threads about funerals. You might like to try some, though you could end up confused since everyone has different views (like they do on this thread)
If you search for 'RE: Memorial Service Threads?' you'll find that the second posting on it has a list of other threads, such as 'What song do you want sung at your funeral'. (Sorry, I can't manage the blue clickies)

There's a huge mixture of stuff - and you probably won't feel any the wiser! It might help if you tell us a bit about what your dad's friend enjoyed doing. Did he have any hobbies/interests?
For instance, if he was a walker then Ewan MacColl's 'Joy of Living' which starts off 'Farewell you northern hills' could be appropriate.
If he liked the sea/sailing then 'the Farewell Shanty' or 'Leave her Johnny leave Her'
More serious or religious? 'Only Remembered' or 'What's the life of a Man'
Just instrumental? 'Ashokan Farewell'
Me, for my funeral I would like 'When All Men Sing' by Keith Scowcroft and Derek Gifford.
Some (but by no means all) of the 'English Folk Songs in this thread could be suitable, depending on the tone that the family want to set. (eg sombre or upbeat)

If you can give us some guidance, it would help. 'Folk' covers such a huge range of stuff! Is there anyone you can ask about what kind of folk music he listened to? Even one CD would give us a clue!

I imagine time is fairly short, but it would be good if whatever was played in his memory and to celebrate his life was 'right for him'. Do post again if you're still stuck - and do let us know what is chosen.

I hope you and you're dad find what you're after