Celebrate the theme of friendship or love during February in honor of Valentine's Day. President's Day is also observed during February; use it as the inspiration to celebrate a theme of leadership or American history during the month.
February is also known as Black History Month. Spend the month learning about and honoring the achievements of African Americans.
The weather also provides plenty of opportunity for thematic activities. Celebrate with a winter theme, or go in the opposite direction: if the weather is cold and snowy, declare February to be Beach Month, and spend the month holding indoor luaus and participating in other summer activities.