You can attach the o-rings pocket by a velcro to the loose end of the counter lung strap to have the necessary o-rings wherever you go.
O-rings pocket includes:
6 x O-ring 16x2 NBR70Sh (for ADV)
2 x O-ring 10,77x2,62 NBR70Sh (for diluent regulator)
2 x O-ring 13,9x2,6 FPM80Sh (for oxygen regulator)