While some of her high school classmates fret over popular clothing trends, 17-year-old Kalsie King said she would gladly forgo whatever “cool points” are associated with the latest fashions, and instead worry about community service. For the past year, King has collected clothing items from classmates, corporations, and family members, with the intention to distribute them to needy families across Greater Boston for Thanksgiving. On Monday, at John D. O’Bryant School of Mathematics & Science in Roxbury, King organized the more than 1,200 pieces of outerwear that she has collected to present to school administrators. King, who is a senior at the school and lives in Hyde Park, will donate the clothes to homeless shelters in Greater Boston.