Last letter! 31ac. Iron extracted from very great amount of jam?(6) ?ARFUL. If it's 'Jarful' I can't parse it. It's one of the clues where the wordplay ignores one letter.
38dn. Reason to switch plan for ultimate rejoicing(10) ?X?L?A?I?N
'Exaltation' and 'exultation' both fit the definition 'rejoicing' but I can't see which it is and why....
13ac. Austrian composer's especially good line for bass (6) LA?N?R The final 'R' is from the second 'R' in 8d: Rolls for large property owners, energetic types(8) T?R??E?S which I assume is TERRIERS...
29dn. French ex-PM wrong about focus on nationalisation? (4). I have BLU?
Leon Blum was a French ex-PM but if that's the answer I'm stumped as to how to parse it....
This query will only make sense to those who have tackled the puzzle. I'm left with 26ac. ?AT and 20dn. ?A?IES which I assume link together and relate to the puzzle's title 'Petite Traveller'?
6d Saint Simon? (Could be a catch) (4) PA?L
26d Fabric mark? A firm's upset with this (5) ?RACK
28d Dip in the loch section, low but rising (4) SOO?...