Big holiday shopping markets in Somerville, including a free Holiday Arts and Crafts Fair from 9 a.m. to 3 p.m. Saturday at the Somerville High School Field House, 81 Highland Ave., with more than 100 handmade-craft vendors (holiday related and otherwise), hourly raffles, live music and lunch food, all benefiting the Somerville High School Girls’ and Boys’ Cross-Country and Track Teams; the free Wintergreen Herbal Market by Herbstalk from 11 a.m. to 5 p.m. Saturday at The Center for Arts at the Armory, 191 Highland Ave., Somerville, with handcrafted herbal products and holiday gifts from more than two dozen local vendors and fun educational demonstrations so you can create your own herbal and plant-inspired gifts at home; and the free Local is for Lovers Small Business Sunday Market from 10 a.m. to 3 p.m. Sunday, again at The Center for Arts at the Armory. This market has food, fun, Knucklebones, live music and some three dozen vendors, including Le Pants King vintage clothing cart.

Indies First Day from 10 a.m. to 5 p.m. Saturday at Porter Square Books, 25 White St., Porter Square. Free.

This second annual books event bring authors and readers together, so local authors can help shoppers pick out the perfect gifts for everyone on their list (or for you). Authors who will be sharing their expertise include Kate Flora in the mystery section and Celeste Ng in fiction from 10 a.m. to noon; Mary Lundquist, whose whimsical work you see above, in “picture books and more” from noon to 2 p.m.; Alexander Danner in graphic novels from 2 to 4 p.m.; and Joan Paquette – an agent and an author specializing in children’s books – from 3 to 4 p.m. Information is here.

Charles Hotel tree lighting from 4 to 6:30 p.m. Saturday at The Charles Hotel, 1 Bennett St., Harvard Square. Free.

This family event includes performances from the Santa Claus Jazz Band and a visit from Santa Claus. Henrietta’s Table will provide complimentary beverages and cookies as children help decorate trees with ornaments and bow ties from Vineyard Vines. The band performs at 5 p.m. and the trees will be lit at 5:30 p.m., followed by an hourlong visit from Santa.

This year’s event, made possible with the help of the Harvard Square Business Association, benefits Cambridge Family & Children’s Service.

Old School Game Show’s Headbanger’s Balls to the Wall Free-For-All at 9 p.m. Saturday at the Davis Square Theatre, 255 Elm St., Somerville. Tickets are $15 for general admission (or $16.52 with an online service fee) or $20 to be a guaranteed contestant (or $21.69 with the service fee).

This is the acid-washed, heavy metal-themed edition of the interactive alt-trivia variety program, with live performances by the Swinging OSGS Band and Cubic Zirconia Dancers, individual-round prizes from local sponsors and a $100 cash prize for the night’s champion.

Enter the theater and you may be randomly (or for more money, not so randomly) selected to take the stage and play in front of the rest of the audience (and against some of them). It’s a live, interactive theater experience “with all the pageantry and analog style of a 1970s television game show,” organizers say, combining “elements of pub trivia, variety specials and comedy sketches to produce a completely unique trivia experience that tests players’ pop culture acumen.” Information is here.

Progressive string concert Mr. Sun at 8 p.m. Sunday at the Davis Square Theatre, 255 Elm St., Somerville. Tickets are $20 general admission (with a $2.09 service fee), $30 premium seating (with a $2.64 fee), or $15 for students (with a $1.82 fee).

Newly formed band Mr. Sun interprets music from across America’s Songbook in an intimate acoustic performance. Along with genres, the band crosses generations, as it includes legendary fiddler Darol Anger, youthful guitar whiz Grant Gordy, bassist Ethan Jodziewicz and mandolinist Joe Walsh. Cello phenom Mila Phelps-Friedl, 16, also performs. Tickets and more info here.