Summer holidays (4th of July, labor day, memorial day) usually involve barbeques and other outdoor activities, so casual clothing is usually the norm. However, there are certain occasions where more formal clothing is required?such as a party through work or hosted at a nice restaurant. For these occasions, business casual attire is appropriate.
Since the summer holidays are more casual affairs, a business casual outfit on the less formal side is recommended. This includes a pair of light colored khakis or chinos, a dress shirt, brown shoes and a matching belt. Darker colors shoes/pants are not usually required for summer holiday occasions.
Watch out for spilling food on your clothes - summer holiday food is usually messy
Summer holiday events usually happen outside - wear lighter fabrics to stay cool
Dress appropriately for the location of the event if it is not outside