(as opposed to out-of-town cheque) means that the cheque was written in the same town where the bank branch, to which the cheque will eventually go back, is located.

Non comp. could be either non compensabile or non compensato. Perhaps you are aware that cheques go a clearing house where debits and credits of each bank are offset against each other. Non compensato would mean "not yet cleared", non compensabile "impossible to clear". To be on the safe side, I suggest that you shorten the word yourself and write "no clear."