Summer Meals Act of 2021 This bill revises provisions related to the Summer Food Service Program (SFSP) of the Department of Agriculture (USDA), which provides meals to children and teens in low-income areas during the summer months when school is not in session. The bill redefines areas in which poor economic conditions exist , where the SFSP may operate, as areas in which at least 40% (currently, 50%) of the children have been determined to be eligible for free or reduced price school meals under the school lunch and breakfast programs. The bill reimburses service institutions (other than school food authorities) for up to one meal and one snack per child each day during after-school hours, weekends, and school holidays during the regular school calendar. Currently, such institutions are reimbursed for meals and snacks served to children over the summer months or to children who are on vacation under a continuous school calendar. USDA must award competitive grants to service institutions to increase participation in the summer food service program for children who lack the ability to access a congregate feeding site through (1) innovative approaches to limited transportation, (2) mobile meal trucks, and (3) any other method or approach that does not require children to access a congregate feeding site. Service institutions that are participating in the summer food service program for children may serve up to three meals, or two meals and one snack, during each day of operation. Currently, this option is reserved for camps and service institutions that serve meals primarily to migrant children.