Birthday Part With Flag Theme

My son's birthday falls on Flag Day this year so I thought it would be a great theme for the party. I need to find a bunch of cheap decorative flags to decorate the house with and I would also like to put one in each of the gift bags for the guests to take home with them. It should be a rather easy and inexpensive party to plan for being that I have a lot of leftover equipment and party decorations from the Fourth of July. I only wish that his birthday would fall on this holiday every year.