There are many collections of popular session tunes in books and on internet websites. Here's a selection of people playing them on YouTube. Why not join in the videos as if you were in a session. The tunes are in no particular order, but all are played in either G or D or a mixture.
Full list
Jenny Lind Polka - played by the Boat Band A part in D / B part in G
Speed the Plough / Princess Royal / Soldier's Joy on D/G box
Three Around Three (A part starts at 0.11) - played in G
Curly-Headed Ploughboy - A part in D / B part in G
(Oh Dem) Golden Slippers - played by Gavin Atkin in G
Country Gardens - played in G
Davy Knick Knack - played in G
Old Joe the Boat is Going Over - played by Gavin Atkin in D
Walter Bulwer's Polka No 1 - played by Gavin Atkin A part in G / B part in D
Oyster Girl - played in G
Uncle Bernard's Polka - played in G
Grandfather's Tune - played by Lester Bailey in D
Jimmy / Jamie Allen - played in G
Haste to the Wedding - played by Anahata in D
The Blue-eyed Stranger, Getting Upstairs and Princess Royal - played by Mark Insley & Jon Doran - in G
Brighton Camp - played in G
Buffalo Girls and Salmon Tails - played in G
The Weaver's March - played in D
The Sloe - played by Anahata in D
Winster Gallop - played in G
Jenny Lind Polka - played by the Boat Band A part in D / B part in G
Speed the Plough / Princess Royal / Soldier's Joy on D/G box
Three Around Three (A part starts at 0.11) - played in G
Curly-Headed Ploughboy - A part in D / B part in G
Galopede - played by Anahata in G on D/G box
(Oh Dem) Golden Slippers - played by Gavin Atkin in G
Country Gardens - played in G
Davy Knick Knack - played in G
Old Joe the Boat is Going Over - played by Gavin Atkin in D
Walter Bulwer's Polka No 1 - played by Gavin Atkin A part in G / B part in D
Oyster Girl - played in G
Uncle Bernard's Polka - played in G
Grandfather's Tune - played by Lester Bailey in D
Jimmy / Jamie Allen - played in G
Haste to the Wedding - played by Anahata in D
The Blue-eyed Stranger, Getting Upstairs and Princess Royal - played by Mark Insley & Jon Doran - in G
Brighton Camp - played in G
Buffalo Girls and Salmon Tails - played in G
The Weaver's March - played in D
The Sloe - played by Anahata in D
Winster Gallop - played in G