The town is holding its first annual Day of Service in honor of Martin Luther King Jr. Day on Monday from 11 a.m. to 4:30 p.m. The event will begin with a Unity Walk from the Battle Green to Cary Hall, where there will be a presentation by several residents and a performance by the Harrington Elementary School Chorus. Participants will then split into groups for a variety of service activities. One group will volunteer at the Waltham YMCA from 1 to 3:30 p.m. to help with its Community Day program, which will provide sports, activities, games, and refreshments for area homeless and low-income families. Another group will serve lunch to seniors at several sites in town from noon to 2 p.m. Another group will make cards for veterans, the homeless, and hospitalized citizens from noon to 3:30 p.m. in Cary Hall. Participants are also invited to donate food, gift cards, books, toys, diapers, and other items to COMPASS for Kids, a local nonprofit organization, and to the Lexington Food Pantry.