Marthabees,

I can only speak about old time jams populated by people who are obsessed with old time (as opposed to folk) music.

First, tunes.

In old time jams you can get a lot of mileage out of being a newbie as long as you let people know. The jammers will be happy to indulge you and play the chestnuts that everybody knows (and which they assume you know), but nobody ever plays, e.g., old joe clark, soldiers' joy, mississippi sawyer, angeline the baker, cumberland gap, june apple, red haired boy, old molly hair, etc. Chances are somebody will remark that they had forgotten how good those chestnuts are. Someone else will probably say that they're old because they're good. etc.

If you are talking about a recurring jam, every one is different. Each group will have a current set of favorites. The list of favorites will change over time as people get tired of some tunes and others capture attention. Old time musicians can be quite faddish.

Don't go to old time jams just to play tunes you know. One function of such jams is to disseminate music. You're expected to learn new tunes by playing them. You are part of an oral/aural tradition when you attend an old time jam, after all. A friend of mine either once said or quoted someone else as saying "In a bluegrass jam everybody knows the tune when they start. In an old time jam everybody knows the tune by the time they finish."

Once you have established yourself as a member of a jam, anything goes.

Second, songs

Once again, every old time jam is different, but most of the ones I have attended tend to be tune jams. Songs definitely takes a back seat to tunes. That said, you can never go wrong with Carter Family songs. Gold Watch and Chain, Orphan Child, Hello Stranger, Wildwood Flower, etc. All old time musicians know and tend to have the highest respect for the Carter Family even if they don't sing much of their stuff.

NOTE that if it is a true old time jam rather than a "folk" jam, it's best not to trot out the folkie favorites like Four Strong Winds until you've established yourself and the group is willing to cut you some slack.