Thats a fair set of rules...only thing i'm not sure about is the 'say if you can't....' Okay, if you've never heard the song before then you cant, and if you have but never tried to learn it then you cant, but sometimes 'cant' is in the mind.....on occasions I've told myself I couldnt play a song and said 'I'm going to sit out' but when made to at least have a go I found I was better than I thought and even if I screwed up nobody cared, me included. Voodoo Chile was a good one for that.

Here's some of my jam songs:

Voodoo Chile
Highway Chile
Red House
Midnight
Dazed and Confused
Whole Lotta Love
Stairway to Heaven
Working Man
Aint gonna give up on Love
Leave my Girl Alone

Many of those seem like obvious choices but thats the idea, lots of people will know them.