The thing to do, of course,is learn lots of songs whuikle you are young. Then when you are old and wizened the long term memory kicks in, and you remember the songs you learned as a babby, and they book you at all the festivals. And if the words come out a bit different from the way they went in, that's just another folk variant to chalk up.

I share moonchild's preference for singing without the words in front of me, and for making up missing bits if necessary. The exception is if it's a song I wrote myself recently, and I haven't sung it in public before. (That's no criticism of those who find written words helpful. It's down to the very different ways our several minds work.)