At year's end it seems everyone has a hand out, and it's not necessarily to shake yours. Now is the time for giving, for acknowledging the attention those around us have provided over the year. But who to tip, and how much? We asked Donn Davis, whose Survival Skills for the Modern Man is due out this June. He suggests giving the mail carrier $20, regardless of what you think of the Postal Service. Give the newspaper delivery guy $15. For doormen and other service personnel in apartments and condos, give $50 to $150 through the management office. In addition, you may want to tip individually, depending on how much you rely on personal attention. Parking lot and health club attendants should get $25 to $40. Maids and nannies get one week's salary, plus Christmas week off.